THE MINERAL BIXBYITE
- Chemical Formula: (Mn, Fe)2O3, Manganese Iron Oxide
- Class: Oxides and Hydroxides
- Uses: A minor ore of manganese and as mineral specimens.
Bixbyite is a rare mineral, but is still well known among collectors. It forms well formed isometric crystals, usually highly modified cubes. It also is associated with several interesting and attractive minerals and has a nice high luster. For these reasons bixbyite is popular among collectors although it only has an unimpressive black color and the crystals are usually small less than 1 centimeter wide.
The associated minerals include pink and clear topaz, pink beryl, spessartine, quartz, hematite, hausmannite, braunite and pseudobrookite. These assortments are found in cavities in rhyolitic rock and make for attractive and much sought after mineral specimens. Especially wonderful bixbyite specimens come from the Thomas Range in Utah.
The crystals of bixbyite are usually cubes. The corners can be modified by octahedral faces which truncate the corners with a single flat face. Also the faces of a dodecahedron can be seen modifying just the corners of the predominant cube with three faces per corner. If all three forms are present the crystal can look rather complex and beautiful.
As an ore of manganese, bixbyite is often under appreciated. When found massive, it is usually associated with other manganese oxides and is impossible to differentiate. Although iron can substitute for the manganese in the structure by over 50%, many bixbyite samples are nearly pure manganese oxide.
- Color is dark black.
- Luster is metallic to submetallic.
- Transparency crystals are opaque.
- Crystal System is isometric; 2/m bar 3
- Crystal Habits include cubes often with octahedral and dodecahedral faces modifying the corners. Also as massive and granular.
- Cleavage is octahedral.
- Fracture is uneven.
- Hardness is 6.5
- Specific Gravity is 4.9 – 5.0 (slightly above average for metallic minerals)
- Streak is black.
- Associated Minerals include beryl, quartz, spessartine, hematite, pseudobrookite, hausmannite, braunite and topaz.
- Notable Occurrences are limited to the Thomas Range, Utah; San Luis Potosi, Mexico; northern Patagonia, Argentina; Gerona, Spain; India; Sweden and South Africa.
- Best Field Indicators are crystal habit, density, hardness, associations and locality.