Blue Topaz Silver Jewllery Erring

Blue Topaz Silver Jewllery Erring 

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Topaz

Topaze, quartz fumé 1.jpg

Topaz crystal on white matrix

General

Category Nesosilicate minerals

Formula

(repeating unit) Al2SiO4(F,OH)2

Strunz classification 9.AF.35

Crystal system Orthorhombic

Crystal class Dipyramidal (mmm) 

H-M symbol: (2/m 2/m 2/m)

Space group Pbnm

Unit cell a = 4.65 Å, b = 8.8 Å, 

c = 8.4 Å; Z = 4

Identification

Color Colorless (if no impurities), blue, brown, orange, gray, yellow, green, pink and reddish pink

Crystal habit Prismatic crystal

Cleavage [001] Perfect

Fracture Subconchoidal to uneven

Mohs scale hardness 8 (defining mineral)

Luster Vitreous

Streak White

Diaphaneity Transparent

Specific gravity 3.49–3.57

Optical properties Biaxial (+)

Refractive index nα = 1.606–1.629

nβ = 1.609–1.631

nγ = 1.616–1.638

Birefringence δ = 0.010

Pleochroism Weak in thick sections X = yellow; Y = yellow, violet, reddish; Z = violet, bluish, yellow, pink

Ultraviolet fluorescence Short UV=golden yellow; Long UV=cream

References

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F, OH)2. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals (Mohs hardness of 8) and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings.