Feb 12 2014
Topaz is a silicate mineral made containing fluorine and aluminum. It was named after Topasos Island in the Red Sea where it was first discovered.
Properties of Topaz
The following are the key mineral properties of Topaz:
- Cell Data
- Space Group: Pbnm
- a = 4.6499(3)
- b = 8.7968(6)
- c = 8.3909(5)
- Z = 4
- Crystal Data
- Orthorhombic
- Point Group: 2/m 2/m 2/m
- Well-formed crystals common, typically morphologically complex, long to short prismatic, to 1.2 m. Prism faces commonly vertically striated, with etch and growth figures on non-prism faces; columnar, compact, massive.
- X-ray Powder Pattern: 2.937 (100), 3.195 (66), 3.693 (60), 2.3609 (45), 2.1049 (44), 3.037 (37), 1.6706 (27)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| Al2O3 |
56.26 |
56.76 |
| SiO2 |
31.93 |
33.00 |
| F |
20.37 |
13.23 |
| -O = F2 |
8.58 |
5.57 |
| H2O+ |
0.19 |
2.67 |
| H2O- |
- |
0.04 |
| Total |
100.17 |
100.13 |
- Optical Properties
- Optical Class: Biaxial (+)
- Pleochroism: In thick sections, X = yellow; Y = yellow, violet, reddish; Z = violet, bluish, yellow, pink
- Orientation: X = a; Y = b; Z = c
- Dispersion: r > v
- α = 1.606-1.634
- β = 1.609-1.637
- γ = 1.616-1.644
- 2V(meas.) = 48°-68°
- Estimated Properties
| Electron density |
Bulk density (electron density)=3.51 g/cm3
note: Specific gravity of Topaz =3.55 g/cm3 |
| Photoelectric |
PETopaz = 1.53 barns/electron
U= PETopaz x ρElectron density= 5.36 barns/cm3 |
| Fermion index |
Fermion index = 0.0074
Boson index = 0.9925 |
| Radioactivity |
Topaz is not radioactive |
How to Identify Topaz
Topaz is either colorless or occurs in red, yellowish brown, yellow, or pale blue color. It is transparent and fluorescent with a perfect cleavage, white streak and vitreous luster.
It fractures in a brittle manner, producing uneven fragments. It can be found as well-formed coarse prismatic crystals. The average density of topaz is 3.55 g/cm3 with a hardness of 8.
Global Distribution
Topaz is commonly found in the following places:
- Mursinka, Ural Mountains, Russia
- Adun-Chilon and Borshchovochnoii Mountains, Nerchinsk district, Siberia
- Schneckenstein, Saxony, Germany
- Xilingeleimeng, Inner Mongolia, China
- Ghundao Hill, near Katlang, Mardan district, Pakistan
- Skardu and Gilgit districts, Pakistan
- Mogok district, Myanmar
- Tanokamiyama, Shiga Prefecture, and the Naegi district, Gifu Prefecture, Japan
- Ouro Preto and near Virgem da Lapa, Minas Gerais, Brazil
- Devils Head, Douglas Co., Colorado
- Thomas Range, Juab Co., Utah
- Lord's Hill, Stoneham, Oxford Co., Maine
- Baldface Mountain, Carroll Co., New Hampshire
- Ramona, San Diego Co., California
- Streeter, Mason Co., Texas
- Tepetate, San Luis Potosi, Mexico
- St. Anne's mine, Miami district, Zimbabwe
- Alto Ligonha district, Mozambique
- Klein Spitzkopje, Namibia
- Jos district, Nigeria
Occurrence of Topaz and Useful Mineral Association
Topaz commonly occurs in cavities and veins within rhyolite and granite. It also occurs in greisen, volatile-rich pneumatolytic hydrothermal fluids and after high-grade metamorphism of aluminous, quartz-rich, and fluorine-bearing sediments.
It is closely associated with quartz, zinnwaldite, cassiterite, fluorite, albite, microcline, beryl and tourmaline.
References