Bixbyite
Manganese iron oxide ((Mn,Fe)2O3)
A black metallic manganese iron oxide famous for sharp cubic crystals, classically found with red beryl and topaz in Utah rhyolite.
- Mohs hardness
- 6-6.5
- Color
- Black to brownish-black with metallic luster
- Type
- mineral
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Overview
Bixbyite is a manganese iron oxide ((Mn,Fe)2O3) celebrated among collectors for its lustrous black, sharply formed cubic crystals. It crystallizes in the isometric system, and well-developed cubes and modified cubes with brilliant metallic luster are its hallmark.
It was named after the American mineral collector Maynard Bixby. (Note: bixbyite should not be confused with bixbite, an old and now-discredited name for red beryl, also linked to Bixby and the same Utah locality.)
Though not a major ore, bixbyite is a striking and well-known species, prized especially for its association with rare gem minerals in volcanic rock.
Formation & geology
Bixbyite forms most famously in cavities and along fractures in rhyolite (a silica-rich volcanic rock), where it crystallizes from manganese- and iron-bearing vapors during the late stages of volcanic cooling. It also occurs in some metamorphic manganese deposits.
The classic locality is the Thomas Range and Topaz Mountain in Utah, USA, where sharp bixbyite cubes occur alongside red beryl, topaz, garnet, and pseudobrookite in rhyolite vugs. Other occurrences include manganese deposits in South Africa, Sweden, India, and Argentina.
How to identify it
Look for small, sharp black to brownish-black cubic (isometric) crystals with a bright metallic to submetallic luster, typically perched in cavities of pinkish rhyolite. The streak is black, and hardness is moderately high (Mohs 6-6.5).
The cubic habit and metallic black color are distinctive, but look-alikes include magnetite (magnetic, octahedral), galena (softer, cleaves into cubes, very dense, lead-gray), and hematite (often platy or earthy). Bixbyite's sharp cubes, black streak, lack of strong magnetism, and rhyolite association help confirm it.
Uses & significance
Bixbyite has little industrial use as an ore because it rarely occurs in quantity; its significance is almost entirely as a collector mineral. Sharp, lustrous cubes from the Thomas Range are highly desirable and command good prices, especially when associated with red beryl or topaz.
It has no gemstone applications (the crystals are opaque and small) and no notable metaphysical tradition. Its main value lies in fine crystallized specimens and in its scientific interest as a vapor-phase mineral in rhyolite.
Frequently asked questions
Is bixbyite the same as red beryl?
No. Bixbyite is a black manganese iron oxide; the discredited name bixbite once referred to red beryl, but they are entirely different minerals despite similar names.
Where is bixbyite found?
Most famously in rhyolite cavities of the Thomas Range and Topaz Mountain in Utah, alongside red beryl and topaz.
What does bixbyite look like?
Small, sharp, lustrous black cubic crystals with a metallic sheen, usually on pinkish volcanic rock.
Is bixbyite magnetic?
It is not strongly magnetic, which helps distinguish it from similarly black magnetite.
Bixbyite guides
In-depth guides for identifying, valuing, and understanding Bixbyite.
Bixbyite identified by the community
Real specimens identified with Rock Identifier.
