Topaz - Occurrence, Properties, and Distribution

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

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit