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.
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.
| Data | Value |
|---|---|
| Name | Dickinsonite |
| Colors | Oil green, olive green, yellowish green, brownish green, brownish. |
| Hardness | 3.5 - 4 |
| Fracture | Uneven |
| Cleavage | Perfect and easy, 1 direction |
| Stone Sizes | Very tiny green gems, less than 1-2 carats, have been cut from Connecticut material. |
| Formula | H2Na6(Mn,Fe,Ca,Mg)14(PO4)12 · H2O. |
| Crystallography | Monoclinic. Crystals tabular, pseudorhombohedral; foliated, micaceous, radiating. |
| Refractive Index | 1.648-1.671 |
| Birefringence | 0.013-0.014 |
| Dispersion | Strong |
| Luminescence | None observed. |
| Luminescence Present | No |
| Absorption Spectrum | Not diagnostic. |
| 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 + |
| Luster | Vitreous; pearly on cleavage. |
| Specific Gravity | 3.38-3.41 |
| Transparency | Transparent to translucent. |
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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