Dickinsonite
This mineral is seldom even mentioned in the gem literature because it is so rare and has been so seldom cut. Faceted gems are practically nonexistent, and would be among the rarest of all cut stones.
Dickinsonite Information
| Data | Value |
|---|---|
| Name | Dickinsonite |
| Colors | Oil green, olive green, yellowish green, brownish green, brownish. |
| Crystallography | Monoclinic. Crystals tabular, pseudorhombohedral; foliated, micaceous, radiating. |
| Refractive Index | 1.648-1.671 |
| Luster | Vitreous; pearly on cleavage. |
| Hardness | 3.5 - 4 |
| Fracture | Uneven |
| Specific Gravity | 3.38-3.41 |
| Birefringence | 0.013-0.014 |
| Cleavage | Perfect and easy, 1 direction |
| Dispersion | Strong |
| Stone Sizes | Very tiny green gems, less than 1-2 carats, have been cut from Connecticut material. |
| Luminescence | None observed. |
| Luminescence Present | No |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
H2Na6(Mn,Fe,Ca,Mg)14(PO4)12 · H2O. |
| Pleochroism |
Pale olive green to pale yellowish green. |
| Optics |
a = 1.648-1.658; β = 1.655-1.662; γ = 1.662-1.671. Biaxial (+), 2V ~90°. |
| Optic Sign | Biaxial + |
Optics: a = 1.648-1.658; β = 1.655-1.662; γ = 1.662-1.671.
Biaxial (+), 2V ~90°.
Occurrence: A secondary phosphate mineral in granite pegmatites.
Branchville, Connecticut; Portland, Connecticut; Poland, Maine.
Comments: This mineral is seldom even mentioned in the gem literature because it is so rare and has been so seldom cut. Faceted gems are practically nonexistent, and would be among the rarest of all cut stones.
Name: After the Rev. William Dickinson in recognition of his interest in the locality where first found.
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