Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Whewellite is one of the most unusual minerals because of its chemical composition and occurrence. It is seldom seen by collectors, and even less thought of as a faceted gemstone. It is really just a curiosity, and there is nothing intriguing about it except its rarity. The dispersion is fairly high but hard to appreciate because of the usual small size of cut gems.
Whewellite Value
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Whewellite Information
| Data | Value |
| Name | Whewellite |
| Crystallography | Monoclinic. Crystals prismatic or equant, also in twins. |
| Colors | Colorless, white, yellowish, brownish. |
| Luster | Vitreous to pearly. |
| Hardness | 2.5-3. |
| Density | 2.19-2.25. |
| Birefringence | O.159—0.163. |
| Cleavage | Good in 1 direction. 2 others distinct. Fracture conchoidal. Brittle. |
| Dispersion | 0.034. |
| Stone Sizes | Crystals are usually very small, colorless. Faceted gems from these will reach a maximum of about 2 carats. |
| Luminescence | None. |
| Spectral | Not diagnostic. |
| Formula | CaC2O4 · H2O (calcium oxalate). |
Optics: a = 1.489; /3 = 1.553; y = 1.649-1.65].
Biaxial (+). 2V: 80°.
Occurrence: Coarse crystals occur in coal seams and concretions (organic origin). Also as a hydrothermal mineral in ore veins.
Elk Creek, South Dakota: fine crystals up to 6 cm in length, among the finest in the world.
Czechoslovakia; France; Hungary: USSR.
Havre, Montana: in septarian concretions.
Burgk. Germany: crystals up to several inches in length.
Comments: Whewellite is one of the most unusual minerals because of its chemical composition and occurrence. It is seldom seen by collectors, and even less thought of as a faceted gemstone. It is really just a curiosity, and there is nothing intriguing about it except its rarity. The dispersion is fairly high but hard to appreciate because of the usual small size of cut gems.
Name: After William Whewell, English natural scientist and philosopher.
