1.
Basalt
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Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually characterized as dark, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured and these phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Mars, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
2.
Groundmass
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The matrix or groundmass of rock is the finer-grained mass of material wherein larger grains, crystals or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic and this porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix, also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock called yellow ground. The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt and it also used to describe the rock material in which a fossil is embedded. All sediments are at first in an incoherent condition, and in this state they may remain for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the floor, yet they are quite friable. The pressure of newer sediments on underlying masses is one cause of this change. More efficiency is generally ascribed to the action of percolating water, the redeposited cementing material is most commonly calcareous or siliceous. Limestones, which were originally a loose accumulation of shells, corals, the change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock, usually also accelerates consolidations. Silica is less soluble in ordinary waters, but even this ingredient of rocks is dissolved and redeposited with great frequency. Others contain fine scales of kaolin or of mica, argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals
3.
Epidote
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Epidote is a calcium aluminium iron sorosilicate mineral. The faces are often deeply striated and crystals are often twinned, many of the characters of the mineral vary with the amount of iron present for instance, the color, the optical constants, and the specific gravity. The color is green, grey, brown or nearly black and it displays strong pleochroism, the pleochroic colors being usually green, yellow and brown. Clinozoisite is green, white or pale rose-red group species containing very little iron, the name, due to Haüy, is derived from the Greek word epidosis which means addition in allusion to one side of the ideal prism being longer than the other. Epidote is an abundant rock-forming mineral, but one of secondary origin and it occurs in marble and schistose rocks of metamorphic origin. It is also a product of alteration of various minerals composing igneous rocks. A rock composed of quartz and epidote is known as epidosite, the perfectly transparent, dark green crystals from the Knappenwand and from Brazil have occasionally been cut as gemstones. Belonging to the same group with epidote are the species piemontite and allanite. Piemontite occurs as small, reddish-black, monoclinic crystals in the mines at San Marcel, near Ivrea in Piedmont. The purple color of the Egyptian porfido rosso antico is due to the presence of this mineral, allanite and dollaseite- have the same general epidote formula and contain metals of the cerium group. The crystallographic and optical characters are similar to those of epidote, the pleochroism is strong with reddish-, yellowish-, and greenish-brown colors. Although not a mineral, allanite is of fairly wide distribution as a primary accessory constituent of many crystalline rocks, gneiss, granite, syenite, rhyolite, andesite. It was first found in the granite of east Greenland and described by Thomas Allan in 1808, allanite is a mineral readily altered by hydration, becoming optically isotropic and amorphous, for this reason several varieties have been distinguished, and many different names applied. Orthite was the name given by Jöns Berzelius in 1818 to a form found as slender prismatic crystals, sometimes a foot in length, at Finbo. Dollaseite is less common, famous from the Ostanmossa mine in the Norberg district of Sweden, dallasite This article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. article name needed
4.
Titus Canyon
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Titus Canyon is a deep, narrow gorge cut into the steep face of the Grapevine Mountains of the Mojave Desert, within Death Valley National Park in southeastern California and southwestern Nevada. The canyon features limestone rock formations, petroglyphs, and native plants, although the Grapevine Mountains were uplifted relatively recently, most of the rocks that make up the range are over half a billion years old. The gray rocks lining the walls of the end of Titus Canyon are Cambrian age limestone. These ancient Paleozoic rocks formed at a time when the Death Valley area was submerged beneath tropical seas, by the end of the Precambrian, the continental edge of North America had been planed off by erosion to a gently rounded surface of low relief. The rise and fall of the Cambrian seas periodically shifted the shoreline eastward, flooding the continent, then regressed westward, the sediments have since been upturned, upfolded, downfolded and folded back onto themselves. Thousands of feet of this limey goo were deposited in the Death Valley region, similar limestone layers may be seen at Lake Mead National Recreation Area and at the bottom of the Grand Canyon. At one of the bends in the canyon, megabreccia can be seen, timbisha Native Americans carved petroglyphs on some of the rock faces in Titus Canyon, especially near natural springs. Another mining town-ghost town dating from the early 20th century, Rhyolite, Nevada, on the Tonopah, several different types of flowers, including the sacred datura, inhabit the area. Desert Bighorn Sheep herds live in Titus Canyon, and the Funeral Mountains, Titus Canyon is located above the east side of Death Valley, within Death Valley National Park. Access by foot from the west via Death Valley, or by vehicles from the east via Nevada, the one-way rough dirt road access begins west of the town of Beatty, Nevada. Places of interest in the Death Valley area Death Valley National Park-related topics Natural history of the Mojave Desert Titus Canyon Visitor Information U. S. National Park Service
5.
Azurite
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Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the locality at Chessy-les-Mines near Lyon. The mineral, a carbonate, has known since ancient times, and was mentioned in Pliny the Elders Natural History under the Greek name kuanos. The blue of azurite is exceptionally deep and clear, and for that reason the mineral has tended to be associated since antiquity with the blue color of low-humidity desert. Azurite is one of the two basic copper carbonate minerals, the other being bright green malachite, simple copper carbonate is not known to exist in nature. Azurite has the formula Cu322, with the copper cations linked to two different anions, carbonate and hydroxide, small crystals of azurite can be produced by rapidly stirring a few drops of copper sulfate solution into a saturated solution of sodium carbonate and allowing the solution to stand overnight. Large crystals are blue, often prismatic. Azurite specimens can be massive to nodular and they are often stalactitic in form. Specimens tend to lighten in color over time due to weathering of the surface into malachite. Azurite is soft, with a Mohs hardness of only 3.5 to 4, the specific gravity of azurite is 3.77 to 3.89. Azurite is destroyed by heat, losing carbon dioxide and water to form black, characteristic of a carbonate, specimens effervesce upon treatment with hydrochloric acid. The optical properties of such as azurite and malachite are characteristic of copper. Many coordination complexes of copper exhibit similar colors, as explained within the context of ligand field theory, the colors result from low energy d-d transitions associated with the d9 metal center. Azurite is unstable in air with respect to malachite. Azurite is also incompatible with media, such as saltwater aquariums. Azurite is not a useful pigment because it is unstable in air and it was however used as a blue pigment in antiquity. Azurite is naturally occurring in Sinai and the Eastern Desert of Egypt and it was reported by F. C. J. Depending on the degree of fineness to which it was ground and it has been known as mountain blue or Armenian stone, in addition it was formerly known as Azurro Della Magna
6.
Malachite
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Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO32. Individual crystals are rare but do occur as slender to acicular prisms, pseudomorphs after more tabular or blocky azurite crystals also occur. The stones name derives from Greek Μολοχίτης λίθος molochitis lithos, mallow-green stone, from μολόχη molōchē, variant of μαλάχη malāchē, the mineral was given this name due to its resemblance to the leaves of the mallow plant. Archeological evidence indicates that the mineral has been mined and smelted to obtain copper at Timna Valley in Israel for over 3,000 years, since then, malachite has been used as both an ornamental stone and as a gemstone. In ancient Egypt the colour green was associated with death and the power of resurrection as well as new life and they believed that the afterlife contained an eternal paradise which resembled their lives but with no pain or suffering, and referred to this place as the ‘Field of Malachite’. Malachite was used as a pigment in green paints from antiquity until about 1800. The pigment is moderately lightfast, very sensitive to acids, and this natural form of green pigment has been replaced by its synthetic form, verditer, among other synthetic greens. Malachite is also used for decorative purposes, such as in the Malachite Room in the Hermitage, which features a huge malachite vase, and the Malachite Room in Castillo de Chapultepec in Mexico City. The Tazza, a large vase, one of the largest pieces of malachite in North America. Malachite often results from the weathering of copper ores, and is found together with azurite, goethite. Except for its vibrant green color, the properties of malachite are similar to those of azurite, Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate. Large quantities of malachite have been mined in the Urals, Russia, ural malachite is not being mined at present, but G. N Vertushkova reports the possible discovery of new deposits of malachite in the Urals. Virtual tour of the Malachite Room Malachite, Colourlex
7.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
8.
Cementation (geology)
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Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains. The new pore-filling minerals form bridges between original sediment grains, thereby binding them together, in this way sand becomes sandstone, and gravel becomes conglomerate or breccia. Cementation occurs as part of the diagenesis or lithification of sediments, cementation occurs primarily below the water table regardless of sedimentary grain sizes present. Large volumes of water must pass through sediment pores for new mineral cements to crystallize. Common mineral cements include calcite, quartz or silica phases like cristobalite, iron oxides, and clay minerals, cementation is continuous in the groundwater zone, so much so that the term zone of cementation is sometimes used interchangeably. Cementation occurs in fissures or other openings of existing rocks and is a process more or less in equilibrium with a dissolution or dissolving process. Cement found on the sea floor is commonly aragonite and can take different textural forms and these textural forms include pendant cement, meniscus cement, isopachous cement, needle cement, botryoidal cement, blocky cement, syntaxial rim cement, and coarse mosaic cement. The environment in each of the cements is found depends on the pore space available. Cements that are found in phreatic zones include, isopachous, blocky, as for calcite cementation, which occurs in meteoric realms, the cement is produced by the dissolution of less stable aragonite and high-Mg calcite. Classifying rocks while using the Folk classification depends on the matrix, beachrock is a type of carbonate beach sand that has been cemented together by a process called synsedimentary cementation. Beachrock may contain meniscus cements or pendant cements, as the water between the narrow spaces of grains drains from the beachrock, a small portion of it is held back by capillary forces, where meniscus cement will form. Pendant cements form on the bottom of grains where water droplets are held, hardgrounds are hard crusts of carbonate material that form on the bottom of the ocean floor, below the lowest tide level. Isopachous cement forms in subaqueous conditions where the grains are surrounded by water. Carbonate cements can also be formed by organisms such as Sporosarcina pasteurii, which binds sand together given organic compounds. Boggs, Sam Jr.2006, Principles of Sedimentology and Stratigraphy, boggs, Sam, Jr.2011, Principles of Sedimentology and Stratigraphy, 5th ed. Chiung-Wen Chou, Eric Seagren, Ahmet Aydilek, Timothy Maugel, bacterially-Induced Calcite Precipitation via Ureolysis, American Society for Microbiology 11 November 2008 Retrieved 20 February 2010
9.
Matrix (geology)
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The matrix or groundmass of rock is the finer-grained mass of material wherein larger grains, crystals or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic and this porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix, also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock called yellow ground. The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt and it also used to describe the rock material in which a fossil is embedded. All sediments are at first in an incoherent condition, and in this state they may remain for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the floor, yet they are quite friable. The pressure of newer sediments on underlying masses is one cause of this change. More efficiency is generally ascribed to the action of percolating water, the redeposited cementing material is most commonly calcareous or siliceous. Limestones, which were originally a loose accumulation of shells, corals, the change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock, usually also accelerates consolidations. Silica is less soluble in ordinary waters, but even this ingredient of rocks is dissolved and redeposited with great frequency. Others contain fine scales of kaolin or of mica, argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals
