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Olmiite is a relatively new mineral, only being officially named as a new species by the IMA in 2006. To date, it is found only in the Kalahari Manganese Field of South Africa. It is unusual for a newly discovered mineral to form is such large and excellent examples, with many well-formed and highly aesthetic examples of this mineral.
Olmiite forms a solid solution series with the much rarer mineral Poldervaartite. Many specimens that had been labelled as Poldervaartite have in fact been Olmiite upon analysis. Olmiite is named after Filippo Olmi, an Italian mineralogist from Florence, Italy. |
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Chemical Formula |
CaMn[SiO3(OH)](OH) |
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Composition |
Basic calcium manganese silicate |
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Color |
Pale yellow, tan, orange-brown, orange, peach, pink, light red, grayish-pink, light gray |
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Streak |
White |
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Hardness |
5 - 5.5 |
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Crystal System |
Orthorhombic |
Crystal Forms
and Aggregates |
In radiating spheres, as botryoidal, acicular, and wheat sheaf crystal groups, in groups of ball-shaped aggregates, and in stacked crystal plates. Individual pyramidal crystals are uncommon. |
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Transparency |
Transparent to nearly opaque |
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Specific Gravity |
3.0 - 3.1 |
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Luster |
Vitreous, pearly |
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Cleavage |
None |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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Other ID Marks |
May be fluorescent red in shortwave ultraviolet light. |
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In Group |
Silicates; Nesosilicates |
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Striking Features |
Color, crystal habits, and locality |
| Environment |
In manganese-rich hydrothermal replacement deposits. |
| Rock Type |
Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
1 |
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Well formed Olmiite examples with good color and form are highly valued by mineral collectors.
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Olmiite has only been found in the Kalahari Manganese Field of South Africa, where it has been found both at the N'Chwaning Mines in Kuruman and the Wessels Mine in Hotazel.
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Bultfonteinite, Calcite, Oyelite, Manganite
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Have a question about Olmiite? Visit our Q&A Community and ask the experts!
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