Editorial Feature

Theophrastite – Occurrence, Properties, and Distribution

Theophrastite is a trigonal-hexagonal scalenohedral emerald green mineral containing nickel, hydrogen, and oxygen. This mineral was named after the first Greek mineralogist Theophrastus.

Properties of Theophrastite

The following are the key properties of theophrastite:

  • Cell Data
    • Space group: P3m1 (synthetic)
    • a = 3.131
    • c = 4.608
    • Z = 1
  • Crystal Data
    • Hexagonal
    • Point group: 3 2/m
    • Minute crystals- finely parallel fibrous, in botryoidal crusts, to 0.5 cm; crystals may be interstratified with other layer-structure minerals.
    • X-ray powder pattern: 2.335 (100), 4.61 (95), 1.755 (50), 2.708 (30), 1.563 (25),1.480 (18),1.336 (10)
  • Chemical Composition
    Elements Content 1 Content 2
    NiO 80.21 80.57
    H2O 19.30 19.43
    Total 99.51 100.00
  • Optical Properties
    • Optical Class: Uniaxial (+)
    • Birefringence: very weak
    • Pleochroism: Weak
    • ω = 1.759-1.760
    • ε = 1.759-1.760
  • Estimated Properties
    Electron density Bulk density (electron density)=3.90 g/cm3
    note: Specific gravity of theophrastite = 3.93 g/cm3
    Photoelectric PETheophrastite = 24.82 barns/electron
    U=PETheophrastite x ρelectron density= 96.81 barns/cm3
    Fermion index Fermion index = 0.0073
    Boson index = 0.9926
    GRapi = 0 (Gamma Ray American Petroleum Institute Units)
    Theophrastite is not radioactive

How to Identify Theophrastite

Theophrastite can be identified in the field by emerald green or blue-green color variations. The appearance of this mineral is transparent. It is a mineral with a glassy luster and a light green streak. The conchoidal fractures in the mineral are brittle with smooth curving surfaces. The density of theophrastite is 4 g/cm3 and hardness is 3.5 (approximate to a copper penny).

Global Distribution

Theophrastite is widely distributed in the following locations:

  • Greece - From the Verrnion district, 50 km west of Thessalonike, Macedonia
  • Scotland - In the Hagdale quarry, Unst, Shetland Islands
  • Canada - Québec, Estrie, Les Sources RCM, Asbestos Jeffrey mine (Jeffrey quarry; Johns-Manville mine)
  • Australia - At the Lord Brassey mine, Heazlewood, Tasmania.

Occurrence of Theophrastite and Useful Mineral Association

Theophrastite is often associated with minerals such as millerite, magnetite, chromite, vesuvianite, chlorite, andradite-grossular, nickeliferous serpentine minerals, calcite (Vermion district, Greece); reevesite, zaratite, honessite, hydrohonessite (Hagdale quarry, Scotland).

Theophrastite occurs as coatings in chromitite in lenses in serpentinites found in Vermion district, Greece and on chromitite in Hagdale quarry, Scotland.


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