Smoky quartz, very common coarse-grained variety of the silica mineral quartz that ranges in colour from nearly black through smoky brown. No distinct boundary exists between smoky and colourless quartz. Its …
Mineral - Hardness, Mohs Scale, Crystalline: Hardness (H) is the resistance of a mineral to scratching. It is a property by which minerals may be described relative to a standard scale of 10 minerals known as …
Chert and flint, very fine-grained quartz (q.v.), a silica mineral with minor impurities. Several varieties are included under the general term chert: jasper, chalcedony, agate (qq.v.), flint, porcelanite, and novaculite. Flint …
Olivine, any member of a group of common magnesium, iron silicate minerals. Olivines are an important rock-forming mineral group. Magnesium-rich olivines are abundant in low-silica mafic and ultramafic igneous rocks and are believed to be the most abundant constituent of the Earth's upper mantle.
MINERAL meaning: 1 : a substance (such as quartz, coal, petroleum, salt, etc.) that is naturally formed under the ground; 2 : a chemical substance (such as iron or zinc) that occurs naturally in certain foods and that is important for good health
Other articles where low quartz is discussed: silica mineral: High quartz (β-quartz): …transition to ordinary quartz (low quartz) on cooling, and all ordinary quartz, when heated above the transition temperature, is transformed into high quartz. The transformation involves displacement of the linkage between the tetrahedrons; no bonds …
Other articles where sagenite is discussed: rutile: …rutile in quartz are called sagenite (from the Greek word for "net"). Hairlike crystals of rutile not included in quartz are rare; the quartz crystals mechanically enclose the rutile during growth. Most fine-quality rutilated quartz comes from Minas Gerais, Brazil; Madagascar; Hanover, New Hampshire; and …
Mineral - Crystal Habit, Aggregation: The external shape (habit) of well-developed crystals can be visually studied and classified according to the various crystal systems that span the 32 crystal classes. The majority of crystal occurrences, however, are not part of well-formed single crystals but are found as crystals grown together in …
Talc, common silicate mineral that is distinguished from almost all other minerals by its extreme softness. Its soapy or greasy feel accounts for the name soapstone given to compact aggregates of talc and other rock-forming minerals. Dense aggregates of high-purity talc are called steatite.
Metamorphic rock - Foliated, Textures, Minerals: The most obvious features of metamorphic rocks are certain planar features that are often termed s-surfaces. The simplest planar features may be primary bedding (akin to the layering in sedimentary rocks). As the rock crystallizes or recrystallizes under directed pressure, new crystals may grow …
Quartz is a mineral that is composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall …
The two most common chemical elements in the Earth's crust, oxygen and silicon, combine to form the mineral quartz, the second most abundant mineral after feldspar.
Quartzite is a metamorphic rock made from quartz sandstone, a sedimentary rock predominantly composed of the silicate mineral quartz. The chemical composite of the quartz minerals is silicon …
The two most common chemical elements in the Earth's crust, oxygen and silicon, combine to form the mineral quartz, the second most abundant mineral after feldspar. Quartz…
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. ... Minerals combine with each other to form rocks. For example, granite consists of the minerals feldspar, quartz, mica, and amphibole in ...
quartz, Second most abundant mineral (after feldspar) in the Earth's crust, present in many rocks. Quartz, which consists of silica, or silicon dioxide (SiO 2 ), has great economic …
Kaolin as found in nature usually contains varying amounts of other minerals such as muscovite, quartz, feldspar, and anatase. In addition, crude kaolin is frequently stained yellow by iron hydroxide pigments.
Agate, common semiprecious silica mineral, a variety of chalcedony that occurs in bands of varying colour and transparency. Agate is essentially quartz, and its physical properties are in general those of that mineral. See silica mineral (table). Agate is found throughout the world. In the United
High quartz, or β-quartz, is the more symmetrical form quartz takes at sufficiently high temperatures (about 573 °C at one atmosphere of pressure), but the relationship is pressure-sensitive. High quartz may be …
Articles from Britannica Encyclopedias for elementary and high school students. sedimentary rock - Children's Encyclopedia (Ages 8-11) sedimentary rock - Student Encyclopedia (Ages 11 and up) ... mainly transported, sand-size minerals such as quartz and feldspar, (2) a detrital matrix of clay or mud, which is absent in "clean" …
Metamorphic rock, any rock that results from the alteration of preexisting rocks in response to changing conditions, such as variations in temperature, pressure, and mechanical stress, and the addition or subtraction of chemical components. The preexisting rocks may be igneous, sedimentary, or other metamorphic rocks.
Formula: SiO2. Colour: Colorless, purple, rose, red, black, yellow, brown, green, blue, orange, etc. Lustre: Vitreous. Hardness: 7. Specific Gravity: 2.65 - 2.66. Crystal System: …
Sandstone, lithified accumulation of sand-sized grains (0.063 to 2 mm [0.0025 to 0.08 inch] in diameter). It is the second most common sedimentary rock after shale, constituting about 10 to 20 percent of the …
silica mineral, Any of the forms of silicon dioxide (SiO2), including quartz, tridymite, cristobalite, coesite, stishovite, melanophlogite, lechatelierite, and ...
Chalcedony, a very fine-grained (cryptocrystalline) variety of the silica mineral quartz (q.v.). A form of chert, it occurs in concretionary, mammillated, or stalactitic forms of waxy lustre and has a compact fibrous structure, a fine splintery fracture, and a great variety of colours—usually
Geology - Earth Composition, Rocks, Minerals: As a discipline, mineralogy has had close historical ties with geology. Minerals as basic constituents of rocks and ore deposits are obviously an integral aspect of geology. The problems and techniques of mineralogy, however, are distinct in many respects from those of the rest of geology, …
Other articles where authigenic mineral is discussed: sedimentary rock: Mineralogical and geochemical composition: …two principal types—namely, detrital and authigenic. Detrital minerals, such as grains of quartz and feldspar, survive weathering and are transported to the depositional site as clasts. Authigenic minerals, like calcite, halite, and gypsum, …
Encyclopædia Britannica, Inc. If a piece of granite, a type of rock, is crushed to powder, one can easily pick out tiny fragments of the separate substances, or minerals, that compose it.One mineral is quartz.The particles often resemble smoky glass. Another is feldspar, next to quartz the most abundant mineral in sandy sediments.
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