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Color: Most commonly black, but can range from colorless to brown, red, orange, yellow, green, blue, violet, pink, or hues in-between. It can also be bi-colored, or even tri-colored. Rarely, it can be found as neon green or electric blue. Crystal habit: Parallel and elongated; acicular prisms, sometimes radiating; massive; scattered grains (in ...
Povondraite is a rare silicate mineral from the tourmaline group with formula: NaFe 3+3 (Fe 3+4 ,Mg 2 ) (BO 3) 3 Si 6 O 18 (OH) 3 O. [2] It is a dark brown to black nearly opaque mineral with a resinous to splendent luster. It crystallizes in the trigonal crystal system as equant, distorted prisms with trigonal pyramid terminations.
References. [ 1][ 2] Carnelian (also spelled cornelian) [ 3] is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral ...
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. Elbaite forms three series, with dravite, with fluor-liddicoatite, and with schorl. Due to these series, specimens with ...
Fluor-uvite [3] is a tourmaline mineral with the chemical formula CaMg 3 (Al 5 Mg) (Si 6 O 18 ) (BO 3) 3 (OH) 3 F. It is a rare mineral that is found in calcium rich contact metamorphic rocks with increased amounts of boron. [4] Uvite is trigonal hexagonal, which means that it has three equal length axes at 120 degrees, all perpendicular to its ...
In plane polarized light (PPL, Fig. 3a) the mineral biotite is light brown to "foxy" red brown with dark circular spots known as “pleochroic halos”. Muscovite is clear and sillimanite is the more acicular-fibrous mineral within the dark zone of the image. In cross polarized light (Fig. 3b) muscovite displays colorful birefringence and ...
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