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Formula (repeating unit) Silica (silicon dioxide, Si O 2) Crystal system: Trigonal: Crystal class: Trapezohedral (32) Space group: ... Amethyst is a violet variety of ...
Amethyst loses its natural violet color when heated to above 200-300°C and turns a color that resembles natural citrine, but is often more reddish or brownish. [9] Unlike natural citrine, the color of heat-treated amethyst is known to come exclusively from trace amounts of iron oxides, specifically hematite and goethite .
Amesite is a mineral with general formula of Mg 2 Al 2 SiO 5 (OH) 4. [3] Amesite crystallizes in the triclinic crystal system. [5] It contains three axes of unequal length, not at right angles. It was first described in 1876 for an occurrence in the Chester Emery Mines, Chester, Hampden County, Massachusetts. It was named for mine owner James Ames.
Ametrine, also known as trystine, golden amethyst, or by the trade name bolivianite, is a variety of quartz with alternating zones of purple and yellow-orange coloration. Its name is a portmanteau of amethyst and citrine. While ametrine is commonly referred to as a combination of these two quartz varieties, some sources claim this is not ...
The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula NaMg 3 (Al,Mg) 6 B 3 Si 6 O 27 (OH), which is in good agreement (except for the OH content) with the endmember formula of dravite as known today. [9] Dravite varieties include the deep green chromium dravite and the vanadium ...
Charoite (/ tʃ æ r oʊ. aɪ t / CHAR-ow-ait) is a rare silicate mineral with the chemical composition K(Ca,Na) 2 Si 4 O 10 (OH,F)•H 2 O, first described in 1978.It is named after the Chara River, despite its being 70 kilometres (43 mi) away from the discovery place.
Although the unit cell is close to being hexagonal in shape ("a" and "c" are nearly equal and β nearly 120°), it is inherently monoclinic and cannot be hexagonal. The crystal structure of coesite is similar to that of feldspar and consists of four silicon dioxide tetrahedra arranged in Si 4 O 8 and Si 8 O 16 rings.
Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li 1.5 Al 1.5)Al 6 Si 6 O 18 (BO 3) 3 (OH) 4, [4] is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.