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78-804: The Hobart Gap is a pass and road through the Watchung Mountains in Northern New Jersey . During the American Revolutionary War , Hessian General Baron Wilhelm von Knyphausen attempted to seize the Hobart Gap, now crossed by present-day Route 24 , in order to attack the American headquarters in Morristown for the British . He was met with successful resistance by General Nathanael Greene , and

156-423: A mantle wedge above the descending slab. The slab releases water vapor and other volatiles as it descends, which further lowers the melting point, further increasing the amount of decompression melting. Each tectonic setting produces basalt with its own distinctive characteristics. The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene . Olivine can also be

234-493: A basalt is diagnostic of how and where it erupted—for example, whether into the sea, in an explosive cinder eruption or as creeping pāhoehoe lava flows, the classic image of Hawaiian basalt eruptions. Basalt that erupts under open air (that is, subaerially ) forms three distinct types of lava or volcanic deposits: scoria ; ash or cinder ( breccia ); and lava flows. Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated , imparting

312-442: A distinctive pillow shape, through which the hot lava breaks to form another pillow. This "pillow" texture is very common in underwater basaltic flows and is diagnostic of an underwater eruption environment when found in ancient rocks. Pillows typically consist of a fine-grained core with a glassy crust and have radial jointing. The size of individual pillows varies from 10 cm up to several metres. When pāhoehoe lava enters

390-427: A flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns . These structures, or basalt prisms , are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed. The size of the columns depends loosely on

468-465: A high content of plagioclase; these are sometimes described as leucobasalts . It can be difficult to distinguish between lighter-colored basalt and andesite , so field researchers commonly use a rule of thumb for this purpose, classifying it as basalt if it has a color index of 35 or greater. The physical properties of basalt result from its relatively low silica content and typically high iron and magnesium content. The average density of basalt

546-621: A lightweight "frothy" texture to the rock. Basaltic cinders are often red, coloured by oxidized iron from weathered iron-rich minerals such as pyroxene . ʻAʻā types of blocky cinder and breccia flows of thick, viscous basaltic lava are common in Hawaiʻi. Pāhoehoe is a highly fluid, hot form of basalt which tends to form thin aprons of molten lava which fill up hollows and sometimes forms lava lakes . Lava tubes are common features of pāhoehoe eruptions. Basaltic tuff or pyroclastic rocks are less common than basaltic lava flows. Usually basalt

624-623: A lower total content of alkali oxides than trachybasalt and most basanites and tephrites. Basalt generally has a composition of 45–52 wt% SiO 2 , 2–5 wt% total alkalis, 0.5–2.0 wt% TiO 2 , 5–14 wt% FeO and 14 wt% or more Al 2 O 3 . Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%. High-alumina basalts have aluminium contents of 17–19 wt% Al 2 O 3 ; boninites have magnesium (MgO) contents of up to 15 percent. Rare feldspathoid -rich mafic rocks, akin to alkali basalts, may have Na 2 O + K 2 O contents of 12% or more. The abundances of

702-575: A matrix of red or gray sandstone. Pyritous copper, also known as chalcopyrite , is not known to exist in ores found in the Watchungs. In the mid-twentieth century, the ability of the Watchungs to hold back the spread of urbanization was greatly reduced with the development of the interstate highway system. Three interstate highways, I-80 , I-280 , and I-78 , were built through the Watchungs, allowing midcentury suburban-style development to become economically feasible within its inner valleys and slopes. Near

780-507: A phenocryst, and when present, may have rims of pigeonite. The groundmass contains interstitial quartz or tridymite or cristobalite . Olivine tholeiitic basalt has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass . Alkali basalts typically have mineral assemblages that lack orthopyroxene but contain olivine. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite

858-692: A response, efforts to conserve the unique landscapes of the Watchungs have been undertaken. The largest of the conservation efforts so far is High Mountain Park Preserve , which at 1,153.7 acres (4.669 km ) sets aside one of the largest tracts of wilderness in the New Jersey Piedmont. The park is known to contain at least one globally imperiled plant, Torrey's mountain mint ( Pycnanthemum torrei ), as well as three other plants endangered within New Jersey. Other large areas of preserved land lie within

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936-523: A significant constituent. Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite , ulvöspinel , and ilmenite . Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt. In tholeiitic basalt , pyroxene ( augite and orthopyroxene or pigeonite ) and calcium -rich plagioclase are common phenocryst minerals. Olivine may also be

1014-440: A square in the center of its downtown. Route 24 was recently redirected around the old road in order to retain the historical downtowns of the colonial villages through which the trail led. The portion of the original path is now labeled Route 124 . 40°43′N 74°19′W  /  40.717°N 74.317°W  / 40.717; -74.317 Watchung Mountains The Watchungs are basalt uplifts, geologically similar to

1092-427: Is 2.9 g/cm , compared, for example, to granite ’s typical density of 2.7 g/cm . The viscosity of basaltic magma is relatively low—around 10 to 10 cP —similar to the viscosity of ketchup , but that is still several orders of magnitude higher than the viscosity of water, which is about 1 cP). Basalt is often porphyritic , containing larger crystals ( phenocrysts ) that formed before the extrusion event that brought

1170-401: Is also produced by some subglacial volcanic eruptions. Basalt is the most common volcanic rock type on Earth, making up over 90% of all volcanic rock on the planet. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below the ocean ridges . Basalt is also the principal volcanic rock in many oceanic islands , including

1248-753: Is considered a key to understanding plate tectonics , its compositions have been much studied. Although MORB compositions are distinctive relative to average compositions of basalts erupted in other environments, they are not uniform. For instance, compositions change with position along the Mid-Atlantic Ridge , and the compositions also define different ranges in different ocean basins. Mid-ocean ridge basalts have been subdivided into varieties such as normal (NMORB) and those slightly more enriched in incompatible elements (EMORB). Isotope ratios of elements such as strontium , neodymium , lead , hafnium , and osmium in basalts have been much studied to learn about

1326-478: Is defined as volcanic rock with a content of between 45% and 52% silica and no more than 5% alkali metal oxides. This places basalt in the B field of the TAS diagram. Such a composition is described as mafic . Basalt is usually dark grey to black in colour, due to a high content of augite or other dark-coloured pyroxene minerals, but can exhibit a wide range of shading. Some basalts are quite light-coloured due to

1404-579: Is rich in titanium compared to augite in tholeiitic basalt. Minerals such as alkali feldspar , leucite , nepheline , sodalite , phlogopite mica, and apatite may be present in the groundmass. Basalt has high liquidus and solidus temperatures—values at the Earth's surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks. The majority of tholeiitic basalts are formed at approximately 50–100 km depth within

1482-402: Is suppressed. Above this depth, submarine eruptions are often explosive, tending to produce pyroclastic rock rather than basalt flows. These eruptions, described as Surtseyan, are characterised by large quantities of steam and gas and the creation of large amounts of pumice . When basalt erupts underwater or flows into the sea, contact with the water quenches the surface and the lava forms

1560-515: Is thought that the Lenape favored the Watchungs for their profusion of natural resources, including abundant freshwater rivers and streams, a variety of forests, and plentiful fish and game. They took advantage of the rich soils and maintained many farm areas where they raised a variety of seasonal crops. The Lenape Trail goes along the edge of the cliffs of the Watchung Mountains and the Lenape used

1638-440: Is too hot and fluid to build up sufficient pressure to form explosive lava eruptions but occasionally this will happen by trapping of the lava within the volcanic throat and buildup of volcanic gases . Hawaiʻi's Mauna Loa volcano erupted in this way in the 19th century, as did Mount Tarawera , New Zealand in its violent 1886 eruption. Maar volcanoes are typical of small basalt tuffs, formed by explosive eruption of basalt through

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1716-455: Is ultimately derived from Late Latin basaltes , a misspelling of Latin basanites "very hard stone", which was imported from Ancient Greek βασανίτης ( basanites ), from βάσανος ( basanos , " touchstone "). The modern petrological term basalt , describing a particular composition of lava -derived rock, became standard because of its use by Georgius Agricola in 1546, in his work De Natura Fossilium . Agricola applied

1794-529: The Clementine mission demonstrate that the lunar maria possess a continuum of titanium concentrations, and that the highest concentrations are the least abundant. Lunar basalts show exotic textures and mineralogy, particularly shock metamorphism , lack of the oxidation typical of terrestrial basalts, and a complete lack of hydration . Most of the Moon 's basalts erupted between about 3 and 3.5 billion years ago, but

1872-618: The Great Trail and always had been used by the Lenape on their route to the Hudson River and south from their hunting grounds in what is now Sussex County . That traditional part of the Great Trail would become Route 24 , and leads from the pass through Chatham , Madison , Morristown , Mendham , and Chester ; it is called Main Street in all but Morristown, the county seat, which is dominated by

1950-487: The North American Wildlife Foundation . It is championed by many organizations among the contemporary communities adjacent to the refuge. The Great Swamp, as well as other swamps retained by the Watchungs, including Great Piece Meadows , constitute the remains of Glacial Lake Passaic . The lake existed during the last ice age, eventually draining as a glacier in the northern Watchungs receded and allowed

2028-484: The Palisades Sill , but it ultimately broke out to the surface through large, episodic eruptions. The Watchung Mountains were formed from these eruptions, consisting of three separate flood basalts that may have filled nearly the entire Newark Basin. Each time the basin filled with basalt , which cooled into blocky trap rock , a period of limited volcanic activity followed, allowing sediment to be deposited on top of

2106-1176: The Paraná Traps in Brazil, the Siberian Traps in Russia , the Karoo flood basalt province in South Africa, and the Columbia River Plateau of Washington and Oregon . Basalt is also prevalent across extensive regions of the Eastern Galilee , Golan , and Bashan in Israel and Syria . Basalt also is common around volcanic arcs, specially those on thin crust . Ancient Precambrian basalts are usually only found in fold and thrust belts, and are often heavily metamorphosed. These are known as greenstone belts , because low-grade metamorphism of basalt produces chlorite , actinolite , epidote and other green minerals. As well as forming large parts of

2184-520: The hypabyssal and plutonic equivalents of basalt. During the Hadean , Archean , and early Proterozoic eons of Earth's history, the chemistry of erupted magmas was significantly different from what it is today, due to immature crustal and asthenosphere differentiation. The resulting ultramafic volcanic rocks, with silica (SiO 2 ) contents below 45% and high magnesium oxide (MgO) content, are usually classified as komatiites . The word "basalt"

2262-524: The lanthanide or rare-earth elements (REE) can be a useful diagnostic tool to help explain the history of mineral crystallisation as the melt cooled. In particular, the relative abundance of europium compared to the other REE is often markedly higher or lower, and called the europium anomaly . It arises because Eu can substitute for Ca in plagioclase feldspar, unlike any of the other lanthanides, which tend to only form cations . Mid-ocean ridge basalts (MORB) and their intrusive equivalents, gabbros, are

2340-455: The surface of a rocky planet or moon . More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro . The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System . For example, the bulk of

2418-457: The Earth's crust, basalt also occurs in other parts of the Solar System. Basalt commonly erupts on Io (the third largest moon of Jupiter ), and has also formed on the Moon , Mars , Venus , and the asteroid Vesta . The dark areas visible on Earth's moon , the lunar maria , are plains of flood basaltic lava flows. These rocks were sampled both by the crewed American Apollo program and

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2496-537: The Earth's crust. Additionally, the Watchungs feature not only blocky aa lava, but also ropey and billowing pahoehoe flows. The magma that generated the Watchungs and the Palisades also formed the intrusive igneous Sourland Mountain in Central New Jersey, as well as a series of smaller outlying volcanic ridges in the region. Cushetunk Mountain , a ring-shaped volcanic mountain between Sourland Mountain and

2574-577: The English colonial period, the rivers and streams of the Watchungs also supported grain, grist, and saw mills. Later, the energy of these rivers would be harnessed for industry, most notably at the Great Falls of the Passaic River , where mechanical and hydroelectric systems exploited the energy of water falling over the face of First Watchung Mountain . Outside of providing gradation to rivers and streams,

2652-706: The Palisades along the Hudson River. In many places, however, the mountains have become sinuous islands of natural landscape within the suburban sprawl covering much of contemporary northeastern New Jersey. Parks, preserves, and numerous historical sites dot the valleys and slopes of the mountains, providing recreational and cultural activities to one of the most densely populated regions of the nation. The two most prominent ridges, known as First Watchung Mountain (the southeastern ridge) and Second Watchung Mountain (the northwestern ridge), stretch for more than forty miles (64 km) from Somerville (in Somerset County ) in

2730-548: The Third Watchung Mountain is confused with its basalt type locality, as on some occasions its entire length is erroneously referred to as Hook Mountain . In addition to the three main ridges of the Watchungs, a smaller fourth ridge exists south of Morristown and west of Third Watchung Mountain. While attaining elevations more than 400 ft (120 m) above sea level, the ridge lacks topographic prominence, only rising to approximately 100 ft (30 m) above

2808-585: The Watchungs from north to south include: Noteworthy summits of the Watchungs include High Mountain , Beech Mountain , and Mount Cecchino in Wayne , which stand at 879 ft (268m), 869 ft (265m) and 755 ft (230m) above sea level. Another notable summit is The Hilltop in Verona , Cedar Grove , and North Caldwell , which peaks at 675 feet (206 m) just east of the water sphere. The Watchung Mountains are said to have been formed millions of years ago when

2886-461: The Watchungs, also served to raise the Metacomets. The Watchungs are composed principally of volcanic basalt , which historically has been used in railroad beds and road construction. In addition to this, in many places the mountains are underlain by red and white sandstone that, at times, has been used in building construction. Mica and calcareous spar often accompany these sandstone beds. Due to

2964-504: The Watchungs, is of the same geologic lineage. The Metacomet Mountains in the Connecticut River Basin, another aborted rift valley, came into existence at approximately the same time as the Watchungs, also through extrusive eruptions. While non-contiguous, the two ranges may be considered geologic cousins, having formed under similar circumstances during the rifting of Pangaea. The same erosive and tectonic forces that elevated

3042-473: The basalt layers are thick and warped into downward dipping trap rock sheets, descending below the current erosional surface of the basin. Notably, the synclines preserve not only the basalt layers, but also some overlying Jurassic sedimentary rock. The largest syncline in the basin, the Watchung syncline, contains the greater portion of the Watchung flood basalts as they appear today. The projecting, eroding edges of

3120-476: The basalt/andesite field of the QAPF diagram. Basalt is further distinguished from andesite by its silica content of under 52%. It is often not practical to determine the mineral composition of volcanic rocks, due to their very small grain size, in which case geologists instead classify the rocks chemically, with particular emphasis on the total content of alkali metal oxides and silica ( TAS ); in that context, basalt

3198-475: The characteristic igneous rocks formed at mid-ocean ridges. They are tholeiitic basalts particularly low in total alkalis and in incompatible trace elements, and they have relatively flat REE patterns normalized to mantle or chondrite values. In contrast, alkali basalts have normalized patterns highly enriched in the light REE, and with greater abundances of the REE and of other incompatible elements. Because MORB basalt

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3276-497: The continent of Africa collided with North America. The original inhabitants of the Watchungs, the Lenape , referred to the mountains as the Wach Unks , or ‘high hills’. Evidence of the Lenape presence in the Watchungs can be seen in numerous camps sites that have been uncovered, mainly along the rivers coursing through mountains and in the small caves abundant in the volcanic rock. It

3354-447: The crust, forming an apron of mixed basalt and wall rock breccia and a fan of basalt tuff further out from the volcano. Amygdaloidal structure is common in relict vesicles and beautifully crystallized species of zeolites , quartz or calcite are frequently found. During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While

3432-533: The end of the twentieth century, I-287 , a semi-circular beltway enclosed the Watchungs within the bulge of suburbia radiating out from New York City. Many pathways of safe passage through the mountains, retained from the time of the Lenapes, were severed and blocked by the highways. Today, along the summits of the Watchungs, talus slope environs as well as globally rare trap rock glade/outcrop communities and their unique species have become threatened by development. As

3510-541: The evolution of the Earth's mantle . Isotopic ratios of noble gases , such as He / He, are also of great value: for instance, ratios for basalts range from 6 to 10 for mid-ocean ridge tholeiitic basalt (normalized to atmospheric values), but to 15–24 and more for ocean-island basalts thought to be derived from mantle plumes . Source rocks for the partial melts that produce basaltic magma probably include both peridotite and pyroxenite . The shape, structure and texture of

3588-537: The fact that First Watchung Mountain is said to be composed of Orange Mountain basalt , while Second Watchung Mountain is composed of Preakness Mountain basalt. The names applied to the basalts are geologic type localities , that is to say, the type of rock found at Orange Mountain is exclusive to all of First Watchung Mountain, while the type of rock found at Preakness Mountain is exclusive to all of Second Watchung Mountain. Similarly to this misinformation about First Watchung Mountain and Second Watchung Mountain, sometimes

3666-568: The flood basalts preserved in the syncline form the three ridges of the Watchung Mountains. Jurassic sedimentary rock layers between and above the three ridges form the Feltville , Towaco , and Boonton formations. Elsewhere in the Newark Basin, smaller synclines preserve the Watchung Outliers , additional fragments of the flood basalts and associated overlying sediments that have survived into

3744-542: The height of the Watchungs has proven useful for other reasons. In the French and Indian War , the military reused the Lenape signal points, as did Washington later. 200 million years ago, magma intruded into the Newark Basin , then an active rift basin associated with the breakup of the supercontinent Pangaea . Initially, the magma was contained within the sedimentary strata of the basin, forming large intrusions such as

3822-410: The history of New Jersey. Parks and reservations from north to south: Basalt Basalt ( UK : / ˈ b æ s ɔː l t , - əl t / ; US : / b ə ˈ s ɔː l t , ˈ b eɪ s ɔː l t / ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low- viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near

3900-708: The islands of Hawaiʻi , the Faroe Islands , and Réunion . The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is the rock most typical of large igneous provinces . These include continental flood basalts , the most voluminous basalts found on land. Examples of continental flood basalts included the Deccan Traps in India , the Chilcotin Group in British Columbia , Canada ,

3978-502: The lake's water to empty out via a gap in the ridges of First Watchung Mountain and Second Watchung Mountain currently occupied by the Passaic River. General awareness of the history and natural environment of Watchungs has been increased through efforts such as the construction and designation of the Lenape Trail . The trail traverses rugged sections of the mountains while at the same time, connecting various historical sites pertinent to

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4056-604: The magma as it decompresses during its approach to the surface; the erupted lava then solidifies before the gases can escape. When vesicles make up a substantial fraction of the volume of the rock, the rock is described as scoria . The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarser) groundmass are more properly referred to either as diabase (also called dolerite) or—when they are more coarse-grained (having crystals over 2 mm across)—as gabbro . Diabase and gabbro are thus

4134-416: The magma to the surface, embedded in a finer-grained matrix . These phenocrysts are usually made of augite, olivine , or a calcium-rich plagioclase, which have the highest melting temperatures of any of the minerals that can typically crystallize from the melt, and which are therefore the first to form solid crystals. Basalt often contains vesicles ; they are formed when dissolved gases bubble out of

4212-704: The mantle. Many alkali basalts may be formed at greater depths, perhaps as deep as 150–200 km. The origin of high-alumina basalt continues to be controversial, with disagreement over whether it is a primary melt or derived from other basalt types by fractionation. Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO 2 and the alkali oxides, i.e., Na 2 O + K 2 O , consistent with their TAS classification . Basalt contains more silica than picrobasalt and most basanites and tephrites but less than basaltic andesite . Basalt has

4290-412: The modern era. Because the majority of the Watchung Mountains are composed of extrusive igneous trap rock, they display characteristic columnar jointing and stacked lava flows. These features are readily noted along the eastern faces of the ridges that often present mural precipices, or vertical escarpments . Similar features also can be seen in the Palisades Sill , although these were formed within

4368-406: The most voluminous of all volcanic formations. Basaltic magmas within Earth are thought to originate from the upper mantle . The chemistry of basalts thus provides clues to processes deep in Earth's interior . Basalt is composed mostly of oxides of silicon, iron, magnesium, potassium, aluminum, titanium, and calcium. Geologists classify igneous rock by its mineral content whenever possible;

4446-410: The oldest samples are 4.2 billion years old, and the youngest flows, based on the age dating method of crater counting , are estimated to have erupted only 1.2 billion years ago. From 1972 to 1985, five Venera and two VEGA landers successfully reached the surface of Venus and carried out geochemical measurements using X-ray fluorescence and gamma-ray analysis. These returned results consistent with

4524-450: The overlooks there as smoke signal locations. With the arrival of Europeans, the same resources that sustained the indigenous peoples served settlers. Trade in furs to European markets, a bounty of game and fish, and native garden produce for the traders was important during the Dutch colonial period when few settlements occurred. Perhaps most importantly with the settlements established during

4602-523: The plains of Venus , which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows ; and basalt is a common rock on the surface of Mars . Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequences of many such flows that can cover hundreds of thousands of square kilometres and constitute

4680-602: The prehistoric Glacial Lake Passaic . The Great Swamp, a large portion of which is designated as the Great Swamp National Wildlife Refuge , is a remnant of this glacial lake and presently is retained by Third Watchung Mountain. Although the Watchungs commonly are described in terms of their east-west ridge arrangement (First Watchung Mountain, Second Watchung Mountain, and Third Watchung Mountain), they also are divided into smaller mountain ranges, as well as various named ridges. Notable ranges and ridges of

4758-410: The previously erupted layer of basalt. In this way, the Newark Basin became layered with alternating strata of Watchung basalt and Jurassic sedimentary rock. Throughout the early Jurassic, the Newark Basin underwent extensive dipping and folding. The western side of the basin plunged deeper into the crust, tilting the strata of the basin to an angle of between 5 and 25 degrees. Localized deformation of

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4836-475: The rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns. The character of submarine basalt eruptions is largely determined by depth of water, since increased pressure restricts the release of volatile gases and results in effusive eruptions. It has been estimated that at depths greater than 500 metres (1,600 ft), explosive activity associated with basaltic magma

4914-411: The relative volume percentages of quartz (crystalline silica (SiO 2 )), alkali feldspar , plagioclase , and feldspathoid ( QAPF ) are particularly important. An aphanitic (fine-grained) igneous rock is classified as basalt when its QAPF fraction is composed of less than 10% feldspathoid and less than 20% quartz, and plagioclase makes up at least 65% of its feldspar content. This places basalt in

4992-595: The robotic Russian Luna program , and are represented among the lunar meteorites . Lunar basalts differ from their Earth counterparts principally in their high iron contents, which typically range from about 17 to 22 wt% FeO. They also possess a wide range of titanium concentrations (present in the mineral ilmenite ), ranging from less than 1 wt% TiO 2 , to about 13 wt.%. Traditionally, lunar basalts have been classified according to their titanium content, with classes being named high-Ti, low-Ti, and very-low-Ti. Nevertheless, global geochemical maps of titanium obtained from

5070-403: The rock at the landing sites being basalts, including both tholeiitic and highly alkaline basalts. The landers are thought to have landed on plains whose radar signature is that of basaltic lava flows. These constitute about 80% of the surface of Venus. Some locations show high reflectivity consistent with unweathered basalt, indicating basaltic volcanism within the last 2.5 million years. Basalt

5148-455: The sea it usually forms pillow basalts. However, when ʻaʻā enters the ocean it forms a littoral cone , a small cone-shaped accumulation of tuffaceous debris formed when the blocky ʻaʻā lava enters the water and explodes from built-up steam. The island of Surtsey in the Atlantic Ocean is a basalt volcano which breached the ocean surface in 1963. The initial phase of Surtsey's eruption

5226-507: The southwest through Morris County , Union County , Essex County , and Passaic County to Mahwah (in Bergen County ) in the northeast. Sometimes the less prominent and discontinuous ridge formed by Long Hill , Riker Hill , Hook Mountain , and Packanack Mountain is referred to as Third Watchung Mountain and lies on the northwestern side of Second Watchung Mountain. A parallel series of gaps through all three mountain ridges extends to

5304-468: The surrounding sedimentary rock. The result of this has been that the exposed edges of the eroding basalt layers have managed to persist longer than the exposed edges of the sedimentary layers, causing them to project prominently above the surrounding surface terrain as high ridges. Today, the flood basalts are preserved in the synclines adjacent to the Ramapo Fault system. It is in these synclines that

5382-521: The surrounding terrain. Only one portion of the ridge is named, a southern section underlying Harding Township known as Lees Hill . All of the ridges lie to the east of the higher Appalachian Mountains , which in northern New Jersey often are referred to as the New York - New Jersey Highlands . Together with the Appalachian Mountains to the west, the Watchungs pen in an area formerly occupied by

5460-648: The term "basalt" to the volcanic black rock beneath the Bishop of Meissen's Stolpen castle , believing it to be the same as the "basaniten" described by Pliny the Elder in AD ;77 in Naturalis Historiae . On Earth, most basalt is formed by decompression melting of the mantle . The high pressure in the upper mantle (due to the weight of the overlying rock ) raises the melting point of mantle rock, so that almost all of

5538-580: The upper mantle is solid. However, mantle rock is ductile (the solid rock slowly deforms under high stress). When tectonic forces cause hot mantle rock to creep upwards, pressure on the ascending rock decreases, and this can lower its melting point enough for the rock to partially melt , producing basaltic magma. Decompression melting can occur in a variety of tectonic settings, including in continental rift zones, at mid-ocean ridges , above geological hotspots , and in back-arc basins . Basalt also forms in subduction zones , where mantle rock rises into

5616-496: The valleys of the Watchungs. Retained within the embrace of Third Watchung Mountain, the Great Swamp National Wildlife Refuge consists of 7,600 acres (31 km2) or approximately 12 square miles (30.4 km²) of varied habitats . The refuge was created through the efforts and donations of a small group of local residents in 1959, the Jersey Jetport Site Association , and a Great Swamp Committee later formed within

5694-504: The volcanic nature of the Watchungs, zeolites , including prehnite , analcime , and stilbite , which form from a reaction of mafic rocks in alkaline environments, can be found along exposed ridge lines. Agate , primarily in the form of chalcedony , and crystalline quartz (sometimes in the form of amethyst ), are prominent in the ancient lava flows of the Watchungs and typically, are seen as embedded nodules along exposed fronts. Datolite , another nodular mineral, has been found embedded in

5772-446: The volcanic rock around the Great Falls . Additionally, jasper and satin spar are known to exist within the northwestern Preakness Range. Copper also can be found in the Watchungs. Near Belleville , ore containing 8% copper was discovered, and a copper mine once operated in the area. Other copper bearing ores have been noted near Paterson . These ores typically contain cuprite (red copper oxide) and/or copper carbonate in

5850-500: The west from near Springfield to the northern boundary of Chatham where the Passic River flows through the Third Watchung Mountain. Often the entireties of First Watchung Mountain and Second Watchung Mountain are erroneously referred to as Orange Mountain and Preakness Mountain . Historically, the names ‘Orange’ and ‘Preakness’ have only been applied to specific sections of these ridges. The confusion appears to have arisen from

5928-496: The western edge of the basin along the Ramapo Fault System formed alternating synclines and anticlines that warped the layers of basalt and sedimentary rock. Erosion began to attack the basin as rifting failed and deposition of new sediments ceased. Over millions of years, erosion ate downward through the tilted rock of the basin, eventually encountering the basalt layers that are significantly more erosion resistant than

6006-735: Was eventually defeated by the Continental Army and the New Jersey Militia at the Battle of Springfield . For thousands of years the pass in the mountain range was an important aspect of the traditional Lenape Minisink Trail . From the pass, the trail led to a landing at the best place to ford what the Native Americans called the Fishawack (the Passaic River ). The trail was a portion of

6084-400: Was highly explosive, as the magma was quite fluid, causing the rock to be blown apart by the boiling steam to form a tuff and cinder cone. This has subsequently moved to a typical pāhoehoe-type behaviour. Volcanic glass may be present, particularly as rinds on rapidly chilled surfaces of lava flows, and is commonly (but not exclusively) associated with underwater eruptions. Pillow basalt

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