May 29 2014
Derbylite is a pitch-black or dark brown colored mineral, having a monoclinic system. It was named after an American geologist, Orville Adelbert Derby, former director of the Brazilian geological survey.
Properties of Derbylite
The following are the key properties of Derbylite:
- Cell Data
- Space Group: P21/m
- a = 7.156–7.160
- b = 14.347–14.354
- c = 4.970–4.980
- β= 104.61°-104.69°
- Z = 2
- Crystal Data
- Monoclinic
- Point Group: 2/m
- As prismatic crystals, to 2mm, elongate along [001], showing many forms, mostly {hk0}; in small grains
- Twinning: On {011} or {153}, commonly as cruciform twins and trillings
- X-ray powder pattern: 2.853 (100), 2.674 (73), 3.186 (43), 3.118 (33), 2.479 (23), 2.393 (23), 3.997 (18)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| TiO2 |
36.6 |
40.2 |
| Fe2O3 |
36 |
31.83 |
| Sb2O3 |
21.5 |
19.8 |
| FeO |
4.44 |
|
| Al2O3 |
3.8 |
|
| H2O |
[1.3] |
[1.24] |
| Cr2O3 |
0.3 |
|
| Total |
[99.5] |
[97.51] |
- Optical Properties
- Optical Class: Biaxial (+)
- Orientation: X = a; Y = b; Z = c
- α = 2.45
- β = 2.45
- γ = 2.51
- 2V(meas.) = ~0°
- Estimated Properties
| Electron density |
Bulk density (electron density) = 4.54 g/cm3
note: Specific gravity of Derbylite = 4.85 g/cm3 |
| Photoelectric |
PEDerbylite = 67.25 barns/electron
U = PEDerbylite x ρElectron density = 305.47 barns/cm3 |
| Fermion index |
Fermion index = 0.02
Boson index = 0.98 |
Radioactivity
|
Derbylite is not radioactive
|
How to Identify Derbylite
Derbylite, commonly observed in black, dark brown or pitch-black colors, is brittle, like glasses and most of the non-metallic minerals. It has an opaque appearance, and its crystals are granular, varying from anhedral to subhedral in the matrix. The mineral has a metallic luster and brownish-black streak.
The average density of derbylite is 4.55 g/cm3, and its relative hardness is 5.
Global Distribution
Derbylite is distributed in the following places:
- Tripuhy, near Ouro Preto, Minas Gerais, Brazil
- Buca della Vena iron mine, north of Stazzema, Apuan Alps, Tuscany, Italy
Occurrence of Derbylite and Useful Mineral Association
Derbylite occurs in cinnabar-bearing placer gravels (Tripuhy, Brazil), microcrystalline barite, and in cavities within metasomatically mineralized dolostones (Buca della Vena mine, Italy).
It is closely associated with barite, dolomite, apuanite, versiliaite, schafarzikite, bournonite, sphalerite, pyrite, muscovite, hematite, rutile, zircon, xenotime, monazite, tripuhyite, and rom´eite.
References