Weloganite
Weloganite is a rare carbonate mineral. Regarding gem quality crystals, it is a one locality mineral that was found at the famous Francon Quarry near the city of Montreal, Quebec, Canada. The quarry has now been reclaimed as a landfill and is not producing any new specimens, making existing specimens true rarities. The mineral is named for famous geologist, W. E. Logan, the founder of Canada’s Geological Survey.
Weloganite forms as crystals that grow into tapered pseudohexagonal prisms that are often completely tapered to a point. Gems are fairly small and typically moderately included and their color can be a very attractive lemon or honey yellow.
| Chemical Formula: | Sr3Na2Zr(CO3)6•3(H2O) |
| Hydrated Strontium Sodium Zirconium Carbonate | |
| Molecular Weight: | 814.16 gm |
| Composition: | Sodium | 5.65 % | Na | 7.61 % | Na2O |
| Strontium | 32.29 % | Sr | 38.18 % | SrO | |
| Zirconium | 11.20 % | Zr | 15.13 % | ZrO2 | |
| Hydrogen | 0.74 % | H | 6.64 % | H2O | |
| Carbon | 8.85 % | C | 32.43 % | CO2 | |
| Oxygen | 41.27 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Triclinic – Pinacoidal |
| Crystal Habit: | Crystals, roughly hexagonal, tapering, the prism faces deeply grooved and striated, withrough pyramidal terminations and a flat pedion, to 10 cm; may be massive. |
| Twinning: | About [103] repeated at 120º. |
| Cleavage: | Perfect on pseudo-{0001} |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 3.5 |
| Density: | 3.20 – 3.22 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Pyroelectric. May be Triboluminescent with blue light (http://www.mindat.org/mesg-6-204391.html) |
| Color: | Lemon-Yellow, pale Yellow, Amber, commonly zoned in basal sections; Colorless in thin fragments. |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous |
| Refractive Index: | 1.558 – 1.646 Biaxial ( – ) |
| Birefringence: | 0.0820 – 0.0900 |
| Dispersion: | Weak |
| Pleochroism: | None |
