BISMITE
Bismite – Bi2O3 – is a relatively common oxide, important as a Bi ore. It is often confused with Bi carbonates and other transparent minerals formed by the alteration of Bi minerals.
Due to its most common habit – earthy, powdery – there is practically no information in the literature about its microscopic characteristics.
It is a polymorph of sphaerobismite.
1. Characteristics
Crystal system: Monoclinic prismatic, pseudo-orthorhombic.
Color: Greenish-gray, greenish-yellow to intense yellow.
Habit: Rare microscopic crystals. Earthy, powdery, granular, colomorphic, compact, massive.
Cleavage: No.
Tenacity: No information available.
Twinning: No.
Fracture: Irregular.
Mohs Hardness: 4.5
Parting: No
Streak: Gray to yellow.
Lustre: Sub-adamantine, matte, earthy.
Diaphaneity: Transparent.
Density (g/cm³): 8.64 – 9.22
2. Geology and Deposits
Bismite typically forms as an oxidation product of primary bismuth minerals, and is often referred to as one of the “bismuth ochres”.
It can form pseudomorphs on bismuthinite.
3. Mineral Associations
In the type locality (Colavi Mine, Potosi, Bolivia) it is associated with native bismuth and cassiterite.
It is associated with common gangue minerals, such as quartz (including smoky quartz variety).
It occurs with other Bi minerals such as native bismuth, bismuthitite, bismuthinite, pucherite, protojoseite, beyerite, bismoclite, kettnerite and walpurgite.
Also with various native elements (gold, arsenic), secondary Cu minerals (brochantite, azurite, mixite), muscovite, uraninite, chalcopyrite, Ni-eskutterudite, native selenium.
4. Transmitted Light Microscopy
In very small fragments, bismite is transparent. It has n=2.42, very high relief, zero birefringence (black interference colors), and is biaxial.
Refraction indices: n = 2.42
PLANE POLARIZED LIGHT – PPL
Color / Pleochroism:
Relief: Very high.
Cleavage: No.
Habits: Earthy, rare crystals.
CROSSED POLARIZED LIGHT – XPL
Birefringence and Interference Colors: Zero (completely black).
Extinction: No information available.
Elongation sign: No information available.
Twins: No.
Zoning: No information available.
CONVERGENT LIGHT
Character: Biaxial.
2V angle: No information available.
Alterations: No information available.
May be confused with: No information available.
5. Reflected Light Microscopy
Sample preparation: No information available.
PLANE POLARIZED LIGHT – PPL
Reflection color: Medium gray with a subtle brownish tint.
Pleochroism: No.
Reflectivity: Low (~12%)
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: It does not exhibit anisotropy.
Internal reflections: Widespread in white, yellow, and green colors.
May be confused with: No information available.
General Characteristics:
No information available.