LUDLAMITE: Idaho (~0.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Ludlamite
Ludlamite has a lovely green color but is too soft for wear. Large crystals are known from only a few localities, and cut stones are extremely rare.
Ludlamite Information
| Data | Value |
|---|---|
| Name | Ludlamite |
| Colors | Apple green, dark green, pale green, greenish white, colorless. |
| Crystallography | Monoclinic. Crystals tabular, wedgeshaped; also granular. |
| Refractive Index | 1.650-1.697 |
| Luster | Vitreous. |
| Hardness | 3.5 |
| Fracture | Conchoidal |
| Specific Gravity | 3.19 |
| Birefringence | 0.038-0.044. |
| Cleavage | Perfect 1 direction |
| Stone Sizes | Ludlamite is seldom cut, and transparent material is always small. The potential may exist for 5-10 carat gems, but most are in the 1-2 carat or smaller range. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Translucent to transparent. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
Fe3(PO4)2 · 4H2O. |
| Optics |
a = 1.650-1.653; β = 1.667-1.675; γ = 1.688-1.697. Biaxial (+), 2V= 82°. |
| Optic Sign | Biaxial + |
Streak: Pale greenish white.
Optics: a = 1.650-1.653; β= 1.667-1.6 75; γ= 1.688-1.697.
Biaxial (+), 2V= 82°.
Occurrence: A secondary mineral in the oxidized zone of ore deposits; also due to the alteration of primary phosphates in granite pegmatites.
New Hampshire.
Cornwall, England; Hagendorf, Germany.
Blackbird Mine, Lemhi County, Idaho: fine crystals up to ½ inch across.
South Dakota: crystalline masses to 12 inches in diameter with 7 mm crystals at Keystone.
Comments: Ludlamite has a lovely green color but is too soft for wear. Large crystals are known from only a few localities, and cut stones are extremely rare.
Name: After Henry Ludlam, of London, English mineralogist and collector.
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