Witherite
Witherite is a rare member of the Aragonite group of minerals that also includes Aragonite and Cerussite. Witherite is very rarely faceted because it is soft, fragile and difficult to polish. It is an interesting mineral in that its crystals always form twins. All members of the Aragonite group can form twins, but Witherite is one member that always forms twins! Witherite gems typically have a pearly luster or internal “sleepiness” similar to Prehnite. Witherite fluoresces a beautiful bluish white under both short wave and long wave UV light with phosphorescence.
Notable occurances of Witherite are Cave-in-Rock, Hardin County, Illinois, USA; Alston Moor, Cumberland and Durham, England; Thunder Bay area, Ontario, Canada.
| Chemical Formula: | Ba(CO3) |
| Barium Carbonate | |
| Molecular Weight: | 197.34 gm |
| Composition: | Barium | 69.59 % | Ba | 77.70 % | BaO |
| Carbon | 6.09 % | C | 22.30 % | CO2 | |
| Oxygen | 24.32 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Pseudohexagonal dipyramidal due to repeated twinning, short prismatic to elongated along [001], {010}, {021}, {012}, other faces commonly rough and horizontally striated, to 12 cm. May be botryoidal to spherical, columnar fibrous, granular, massive. |
| Twinning: | On {110}, universal |
| Cleavage: | Distinct on {010}, poor on {110} and {012} |
| Fracture: | Sub-Conchoidal to Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 3.0 – 3.5 |
| Density: | 4.22 – 4.31 (g/cm3) |
| Luminescence: | Bluish white under SW UV with phosphorescence (green and yellow in material from England); bluish white under LW UV with phosphorescence (yellowish in material from England); Fluoresces in X-rays |
| Radioactivity: | Not Radioactive |
| Health Warning: | CAUTION: Barium Carbonate is toxic if ingested. Handling of Witherite is not a major cause of concern as long as you avoid breathing in dust and wash your hands after handling. |
| Other: | Effervesces in dilute HCl solutions; soluble in dilute HCl |
| Color: | Colorless, white, pale gray, may be tinted pale yellow, pale brown, or pale green; colorless in transmitted light |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous; resinous on fractures |
| Refractive Index: | 1.529 – 1.677 Biaxial ( – ) |
| Birefringence: | 0.1480 |
| Dispersion: | Very weak; r > v |
| Pleochroism: | None |
