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36-616: The Vasquez Formation was described as "Vasquez Series" by Sharp in 1935, and further described by Jahns (1939). The formation crops out in the eponymous Vasquez Rocks , part of the Los Angeles Basin . The formation was deposited in a series of minibasins between the San Gabriel and San Andreas Faults . The Vasquez Formation unconformably overlies Triassic basement of the Mount Lowe intrusive series , and localized

72-689: A continuous line along the top edge with lines protruding down; outcrops have a continuous line around each area of bare rock. An outcrop example in California is the Vasquez Rocks , familiar from location shooting use in many films , composed of uplifted sandstone . Yana is another example of outcrops, located in Uttara Kannada district in Karnataka , India . Zircon Zircon ( / ˈ z ɜːr k ɒ n , - k ən / )

108-627: A growing array of specialty applications as zirconia and zirconium chemicals, including in nuclear fuel rods, catalytic fuel converters and in water and air purification systems. Zircon is one of the key minerals used by geologists for geochronology . Zircon is a part of the ZTR index to classify highly- weathered sediments . Transparent zircon is a well-known form of semi-precious gemstone , favored for its high specific gravity (between 4.2 and 4.86) and adamantine luster . Because of its high refractive index (1.92) it has sometimes been used as

144-546: A record of relative changes within geologic strata . Accurate description, mapping, and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as the law of superposition , the principle of original horizontality , principle of lateral continuity , and the principle of faunal succession . On Ordnance Survey maps in Great Britain , cliffs are distinguished from outcrops: cliffs have

180-400: A rich and varied record of geological processes. Currently, zircons are typically dated by uranium-lead (U-Pb), fission-track , and U+Th/He techniques. Imaging the cathodoluminescence emission from fast electrons can be used as a prescreening tool for high-resolution secondary-ion-mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest for isotope analysis. This

216-457: A strong but unproven potential for paleontological interest. The formation on United States Geological Survey (USGS) maps is subdivided into four units based on its lithological composition; Outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets . Outcrops do not cover

252-403: A substitute for diamond , though it does not display quite the same play of color as a diamond. Zircon is one of the heaviest types of gemstone. Its Mohs hardness is between that of quartz and topaz, at 7.5 on the 10 point scale, though below that of the similar manmade stone cubic zirconia (8-8.5). Zircons may sometimes lose their inherent color after long exposure to bright sunlight, which

288-542: A zircon is cut with this axis perpendicular to its table, birefringence may be reduced to undetectable levels unless viewed with a jeweler's loupe or other magnifying optics. The highest grade zircons are cut to minimize birefringence. The value of a zircon gem depends largely on its color, clarity, and size. Prior to World War II, blue zircons (the most valuable color) were available from many gemstone suppliers in sizes between 15 and 25 carats; since then, stones even as large as 10 carats have become very scarce, especially in

324-488: Is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium . Its chemical name is zirconium(IV) silicate , and its corresponding chemical formula is Zr SiO 4 . An empirical formula showing some of the range of substitution in zircon is (Zr 1–y , REE y )(SiO 4 ) 1–x (OH) 4x–y . Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements . For example, hafnium

360-525: Is about 0.1–0.3 mm (0.0039–0.0118 in), but they can also grow to sizes of several cm, especially in mafic pegmatites and carbonatites . Zircon is fairly hard (with a Mohs hardness of 7.5) and chemically stable, and so is highly resistant to weathering. It also is resistant to heat, so that detrital zircon grains are sometimes preserved in igneous rocks formed from melted sediments. Its resistance to weathering, together with its relatively high specific gravity (4.68), make it an important component of

396-456: Is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system . The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green. The name derives from the Persian zargun , meaning "gold-hued". This word is changed into " jargoon ", a term applied to light-colored zircons. The English word "zircon"

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432-457: Is compromised, and the color changes. Zircon occurs in many colors, including reddish brown, yellow, green, blue, gray, and colorless. The color of zircons can sometimes be changed by heat treatment. Common brown zircons can be transformed into colorless and blue zircons by heating to 800 to 1,000 °C (1,470 to 1,830 °F). In geological settings, the development of pink, red, and purple zircon occurs after hundreds of millions of years, if

468-545: Is derived from Zirkon , which is the German adaptation of this word. Yellow, orange, and red zircon is also known as " hyacinth ", from the flower hyacinthus , whose name is of Ancient Greek origin. Zircon is common in the crust of Earth. It occurs as a common accessory mineral in igneous rocks (as primary crystallization products), in metamorphic rocks and as detrital grains in sedimentary rocks . Large zircon crystals are rare. Their average size in granite rocks

504-601: Is dominated by sandstone clasts from the San Francisquito Formation, the Vasquez Formation sandstone contains significantly more quartz and sedimentary lithics. The Vasquez Formation has been interpreted to represent primarily proximal alluvial-fan deposits. The lenses of granitoid crackle and jigsaw breccia in the Vasquez Formation north of Blue Ridge were concluded to be rock-avalanche deposits. The thin interval of thinly bedded limestone atop

540-490: Is done using an integrated cathodoluminescence and scanning electron microscope. Zircons in sedimentary rock can identify the sediment source. Zircons from Jack Hills in the Narryer Gneiss Terrane , Yilgarn Craton , Western Australia , have yielded U-Pb ages up to 4.404 billion years, interpreted to be the age of crystallization, making them the oldest minerals so far dated on Earth. In addition,

576-456: Is mainly consumed as an opacifier , and has been known to be used in the decorative ceramics industry. It is also the principal precursor not only to metallic zirconium , although this application is small, but also to all compounds of zirconium including zirconium dioxide ( ZrO 2 ), an important refractory oxide with a melting point of 2,717 °C (4,923 °F). Other applications include use in refractories and foundry casting and

612-583: Is present near the base of the section, in places capped by thinly bedded tan limestone . Clasts of the Jurassic granitoid were encountered in the Vasquez Formation. North of Blue Ridge, the Vasquez Formation also lies depositionally atop granitoid, possibly with some intervening San Francisquito Formation in places. The Vasquez Formation north of Blue Ridge contains lenses of very poorly sorted, very angular, matrix-poor megabreccias, interbedded with Vasquez Formation conglomerate and sandstone. These deposits fit

648-716: Is unusual in a gemstone. It is immune to acid attack except by sulfuric acid and then only when ground into a fine powder. Most gem-grade zircons show a high degree of birefringence which, on stones cut with a table and pavilion cuts (i.e., nearly all cut stones), can be seen as the apparent doubling-up of the latter when viewed through the former, and this characteristic can be used to distinguish them from diamonds and cubic zirconias (CZ) as well as soda-lime glass, none of which show this characteristic. However, some zircons from Sri Lanka display only weak or no birefringence at all, and some other Sri Lanka stones may show clear birefringence in one place and little or none in another part of

684-933: The Jurassic syenite occurring in the area. The formation, comprising some rhyodacite and rhyolite , is overlain by the Paradise Springs Formation in the Punchbowl Block and the Tick Canyon strata in the Soledad Basin , separated by an angular unconformity . The formation is considered equivalent to the Plush Ranch and Diligencia Formations . In the Soledad Basin and the San Andreas Fault Zone ,

720-743: The bedrock in situ for geologic analysis and creating geologic maps . In situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Some of the types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, are structural geology features orientations (e.g. bedding planes, fold axes, foliation ), depositional features orientations (e.g. paleo-current directions, grading, facies changes), paleomagnetic orientations. Outcrops are also very important for understanding fossil assemblages, and paleo-environment, and evolution as they provide

756-501: The oxygen isotopic compositions of some of these zircons have been interpreted to indicate that more than 4.3 billion years ago there was already liquid water on the surface of the Earth. This interpretation is supported by additional trace element data, but is also the subject of debate. In 2015, "remains of biotic life " were found in 4.1-billion-year-old rocks in the Jack Hills of Western Australia. According to one of

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792-530: The weathering rate such as on steep hillsides, mountain ridges and tops, river banks, and tectonically active areas. In Finland , glacial erosion during the last glacial maximum (ca. 11000 BC), followed by scouring by sea waves, followed by isostatic uplift has produced many smooth coastal and littoral outcrops. Bedrock and superficial deposits may also be exposed at the Earth's surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of

828-441: The crystal has sufficient trace elements to produce color centers . Color in this red or pink series is annealed in geological conditions above temperatures of around 400 °C (752 °F). Structurally, zircon consists of parallel chains of alternating silica tetrahedra (silicon ions in fourfold coordination with oxygen ions) and zirconium ions, with the large zirconium ions in eightfold coordination with oxygen ions. Zircon

864-480: The definitions of "crackle breccia facies" and "jigsaw breccia facies". The sorting, rounding, grading, and matrix within Vasquez conglomerate suggest deposition by debris-flow and hyperconcentrated-flow mechanisms. Where Vasquez Formation conglomerate is dominated by granitoid and volcanic clasts, the sandstone composition is dominated by feldspar , especially plagioclase. While where the Vasquez Formation conglomerate

900-552: The formation is described by the United States Geological Survey (USGS) as: Early Miocene to Oligocene? yellowish and reddish sandstone, conglomerate, and interbedded andesite-basalt, lying on pre-Tertiary crystalline basement rocks and unconformably below strata of Tick Canyon Formation ; total thickness as much as 3,810 metres (12,500 ft). The formation includes numerous beds and lenses of megabreccia , many monolithologic. The formation represents

936-408: The heavy mineral fraction of sandstones. Because of their uranium and thorium content, some zircons undergo metamictization . Connected to internal radiation damage, these processes partially disrupt the crystal structure and partly explain the highly variable properties of zircon. As zircon becomes more and more modified by internal radiation damage, the density decreases, the crystal structure

972-439: The interbedded trachyandesite was interpreted as lacustrine , likely the result of ponding against the volcanic flows. The high relative abundance of trachyandesite and rhyolite clasts immediately up section of the trachyandesite flows suggests that the rhyolite clasts are from deposits closely related to, and thus broadly coeval with, the trachyandesite flows. If so, then the 24.4 ± 0.9 Ma age determined by Coffey et al. in 2019 for

1008-400: The majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by soil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed through erosion or tectonic uplift , the rock may be exposed, or crop out . Such exposure will happen most frequently in areas where erosion is rapid and exceeds

1044-464: The most desirable color varieties. Synthetic zircons have been created in laboratories. They are occasionally used in jewellery such as earrings. Zircons are sometimes imitated by spinel and synthetic sapphire , but are not difficult to distinguish from them with simple tools. Zircon from Ratanakiri province in Cambodia is heat treated to produce blue zircon gemstones, sometimes referred to by

1080-530: The paleogeography of the area has been interpreted as an existing high to the southeast of the Soledad Basin, where the alluvial fans prograded towards the northwest. The formation was deposited before the San Gabriel Fault became active, during the deposition of the Mint Canyon and Castaic Formations . Although the formation to date has not provided fossil remains, the Vasquez Formation has

1116-532: The rhyolite clasts should approximate the age of the trachyandesite flows, and thus the age of the interbedded strata. Therefore, deposition of the Vasquez Formation in the Punchbowl Block probably began approximately 25–24 Ma or earlier. Zircons found in the overlying Tick Canyon strata and interpreted as coming from the Vasquez volcanics were dated at 25.3 ± 0.1 Ma. In the Early Miocene, around 21 Ma,

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1152-444: The same cut stone. Other gemstones also display birefringence, so while the presence of this characteristic may help distinguish a given zircon from a diamond or a CZ, it will not help distinguish it from, for example, a topaz gemstone. The high specific gravity of zircon, however, can usually separate it from any other gem and is simple to test. Also, birefringence depends on the cut of the stone in relation to its optical axis . If

1188-517: The stratigraphically lowermost non-marine strata. The Vasquez Formation is composed primarily of bright-red conglomerate and sandstone. The conglomerate exhibits low degrees of rounding and sorting, a muddy matrix, and, commonly, reverse grading. South of Blue Ridge, the Vasquez Formation nonconformably overlies granitoid , although the base of the section is excised by the Blue Ridge Fault along much of its length. Interbedded trachyandesite

1224-463: The trade name cambolite . Zircon is a common accessory to trace mineral constituent of all kinds of igneous rocks, but particularly granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircon can occasionally be found as a trace mineral in ultrapotassic igneous rocks such as kimberlites , carbonatites, and lamprophyre, owing to

1260-477: The unusual magma genesis of these rocks. Zircon forms economic concentrations within heavy mineral sands ore deposits , within certain pegmatites , and within some rare alkaline volcanic rocks, for example the Toongi Trachyte, Dubbo, New South Wales Australia in association with the zirconium-hafnium minerals eudialyte and armstrongite. Australia leads the world in zircon mining, producing 37% of

1296-550: The world total and accounting for 40% of world EDR ( economic demonstrated resources ) for the mineral. South Africa is Africa's main producer, with 30% of world production, second after Australia. Zircon has played an important role during the evolution of radiometric dating . Zircons contain trace amounts of uranium and thorium (from 10 ppm up to 1 wt%) and can be dated using several modern analytical techniques. Because zircons can survive geologic processes like erosion , transport, even high-grade metamorphism , they contain

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