MILARITE: Tsumeb, Namibia (0.53). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Milarite was originally known as a green mineral, until fine yellow crystals were discovered in Mexico in 1968. Larger Mexican crystals have transparent areas and have been faceted into small gems of pleasant appearance but great rarity.
| Data | Value |
|---|---|
| Name | Milarite |
| Colors | Colorless, pale green, yellowish, yellowish green. |
| Crystallography | Hexagonal. Crystals prismatic and tabular; in grains. |
| Refractive Index | 1.529-1.551 |
| Luster | Vitreous. |
| Hardness | 5.5-6 |
| Fracture | Conchoidal to uneven |
| Specific Gravity | 2.46-2.61 |
| Birefringence | 0.003 |
| Cleavage | None |
| Stone Sizes | Crystals occur up to about 4 cm across, but facetable areas in such crystals are very small. Stones over 1 carat could be considered large for the species. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Transparent to opaque. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
K2Ca4Be4Al2Si24O60·H2O. |
| Optics |
o = 1.532-1.551: e = 1.529-1-548. Uniaxial (-). |
| Optic Sign | Uniaxial - |
Osumilite Group.
Occurrence: In vugs in granites and syenites: hydrothermal veins.
St. Gotthard, Switzerland: green crystals.
Guanajuato, Mexico: yellow and yellow green crystals on matrix, flat, platelike.
Africa: occasional small facetable crystals found.
Comments: Milarite was originally known as a green mineral, until fine yellow crystals were discovered in Mexico in 1968. Larger Mexican crystals have transparent areas and have been faceted into small gems of pleasant appearance but great rarity.
Name: After the Val Milar, Switzerland, because the mineral was (mistakenly) thought to have occurred there.
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