Quartz

It has a trigonal syngony , a point group D ₃ ( in the Schönflis designation ) or 32 (in the international designation). Crystals are hexagonal pseudo-hexagonal prisms , from one end (less often from both) crowned with a hexagonal or trihedral pyramidal head, combining the faces of two rhombohedrons . Often toward the head, the crystal gradually narrows. On the faces of the prism is characterized by transverse hatching. Single crystals of quartz can have right and left forms.

In magmatic and metamorphic rocks, quartz forms irregular isometric grains fused with grains of other minerals; voids and tonsils in effusion are often encrusted with its crystals.

In sedimentary rocks - nodules , veins, secretions (geodes), brushes of small short-prismatic crystals on the walls of voids in limestone, etc. Also fragments of various shapes and sizes, (crushed stone), (pebbles) pebbles , sand (aleurites).

In its pure form, quartz is colorless or white in color due to internal cracks and crystalline defects . Impurities and microscopic inclusions of other minerals, mainly iron oxides, give it the most diverse color . It has many varieties, among which are almost black morion , purple amethyst , yellow citrine , etc. The reasons for the coloring of some varieties of quartz have their own specific nature.

Often forms doubles .

It is soluble in hydrofluoric acid and alkali melts.

The melting point is 1713-1728 ° C (due to the high viscosity of the melt, the determination of the melting temperature is difficult, various data exist).

Dielectric and piezoelectric .

It belongs to the group of glass-forming oxides, that is, it can be the main component of glass . Pure silica one-component silica glass is obtained by melting rock crystal, vein quartz and silica sand. Silicon dioxide has a polymorphism . Stable under normal conditions, the polymorphic modification is α-quartz (low temperature). Accordingly, β-quartz is called a high-temperature modification.

Quartz has several polymorphic modifications, which are independent mineral species:

• cristobalite
• tridymite
• coesitis
• stishovite (formed at very high pressure, first obtained artificially, then found in the Arizona meteorite crater.

• Aventurine is a greenish mineral without the inclusion of sparks. Not to be confused with artificial aventurine - a kind of Murano glass (Italy), - a flickering brownish-red artificial stone, (flickering is caused by inclusions of metal grains)
• Agate is a layered-banded variety of chalcedony.
• Amethyst is purple.
• Ametrine - yellow-violet, crystals with zonal color of amethyst and citrine flowers.
• Bingemite is an iridescent quartz with goethite inclusions.
• Volosatik is rock crystal with inclusions of fine needle crystals of rutile , tourmaline and / or other minerals forming needle crystals.
• Rhinestone - crystals of colorless transparent quartz.
• Flint - dense massive aggregates of silica of variable composition, consisting of crystalline (quartz, chalcedony) and amorphous silica in sedimentary rocks. It is often colored with iron and manganese oxides in different colors, with smooth transitions between them.
• Morion is black.
• Overflow - consist of alternating layers of microcrystals of quartz and chalcedony, are never transparent.
• Prasem - green (due to actinolite inclusions).
• Prasiolite - onion-green, rarely found in nature ^[4] , also obtained by calcining an amethyst.
• Rauchtopaz (smoky quartz) - light gray or light brown.
• Rose quartz is pink.
• Chalcedony is a cryptocrystalline fine-fiber variety. Translucent or translucent, color from white to honey-yellow. Forms spherulites ^[5] , spherulitic crusts, pseudostalactites ^[6] or continuous massive formations.
• Citrine is a lemon yellow.
• Sapphire quartz is a bluish, coarse-grained aggregate of quartz.
• Cat's eye - white, pinkish, gray quartz with the effect of light tint.
• Hawkeye is a silica aggregate of bluish-gray amphibole .
• Tiger's eye - similar to the falcon eye, but golden brown.
• Onyx - brown with white and black patterns, red-brown, brown-yellow, honey, white with yellowish or pinkish streaks. Onyx is particularly characterized by plane-parallel layers of different colors.
• The heliotrope is an opaque dark green variety of cryptocrystalline silica, mostly fine-grained quartz, sometimes mixed with chalcedony, iron oxides and hydroxides and other minor minerals, with bright red spots and stripes.

Quartz is formed during various geological processes.

It crystallizes directly from magma of an acidic composition. It contains both intrusive ( granite , diorite ) and effusive ( rhyolite , dacite ) rocks of acidic and medium composition, can be found in igneous rocks of the main composition (quartz gabbro ). According to measurements by geobarothermometry , quartz is precipitated in granites at Т ≈ 700 ° C.

In volcanic rocks of acidic composition, it often forms porphyry phenocrysts. Its release temperature may exceed 1000 ° C.

Quartz crystallizes from fluid-enriched pegmatite magmas and is one of the main minerals of granite pegmatites . In pegmatites, quartz forms intergrowths with potassium feldspar (pegmatite itself), the internal parts of pegmatite veins are often composed of pure quartz (quartz core).

Quartz is the main mineral of apogranite metasomatites - greisen .

During the hydrothermal process , quartz and crystalline veins are formed. Often beautiful geodes made of quartz minerals, often with an agate shell.

Widely distributed in sedimentary strata (for example, in the Moscow Region ), it is often found in limestones , dolomites, and other rocks in the form of nodules , geodes , fine crystalline crusts, and veins in cracks. When weathering under surface conditions, quartz is stable and accumulates in placers of various genesis (coastal-marine, aeolian, alluvial , etc.) in the form of rounded pebbles . The main mineral is sand and sandstone , and deposits of monomineral quartz sand are of great industrial importance.

A method for the synthesis of artificial quartz by the hydrothermal method has been developed. The advantage of synthetic quartz for industry is the uniform distribution of impurities, higher chemical purity. Of great importance is the fact that the result of the cultivation is single crystals, which in their properties are more suitable for use as piezoelectric quartz than the widely distributed twin crystals in nature. For the jewelry industry, the synthesis method is also important, because it allows you to get quartz of any color and desired saturation, if necessary, even with transitions from one color to another. Artificial crystals are given green (very rare in nature) and blue (there are no natural analogues) colors; blue quartz, which does not exist in nature, is grown. The production of synthetic quartz crystals is developing in Gus-Khrustalny , Shilovo-Ryazan region , Yuzhnouralsk.

Quartz is used in optical devices, in ultrasound generators, in telephone and radio equipment (like a piezoelectric ), in electronic devices ( quartz resonator is sometimes called “quartz” in the technical slang - a component of devices for stabilizing the frequency of electronic generators ). Large quantities are consumed by the glass and ceramic industries (rock crystal and pure quartz sand ). It is also used in the production of siliceous refractories and quartz glass . Many varieties are used in jewelry.

• Quartz sand
• Quartz Artificial Stone

• Quartz at Geowikipedia
• About quartz (Russian)
• Quartz in the webmineral.com database
• Quartz and its varieties (Russian)
• Quartz in the catalogmineralov.ru database
• Quartz technology .