Meionite
Meionite is a calcium aluminum silicate carbonate mineral that is a member of the Scapolite Group of minerals that also includes Marialite. Scapolite is also considered to be the name of the series between Marialite, which is the sodium chloride rich member and Meionite, the calcium carbonate-rich member. Distinguishing these two minerals from each other is difficult as they differ only slightly in density and index of refraction, increasing in both with increasing calcium content. For this reason, Scapolite is the name commonly used to describe minerals and gems within the series.
Meionite was named in 1801 by Rene Just Haüy from the Greek word for less, in reference to the less acute pyramidal form compared with Vesuvianite.
Locations for Meionite: most specimens are intermediate in the series, see also marialite; some localities for highly calcic material include: at Monte Somma and Vesuvius, Campania, Italy. Around the Laacher See, Eifel district, Germany. From Pargas and Pusunsaari, Finland. At Slyudyanka, near Lake Baikal, Siberia, Russia. From Gooderham, Ontario, and Grenville, Quebec, Canada. At Rossie, St. Lawrence County, New York; Bolton, Worcester County, Massachusetts; and Cutcane Creek, Fannin County, Georgia, USA.
| Category: | Scapolite group |
| Chemical Formula: | Ca4Al6Si6O24(CO3) |
| Calcium Aluminum Silicate Carbonate | |
| Molecular Weight: | 934.71 gm |
| Composition: | Calcium | 17.15 % | Ca | 24.00 % | CaO |
| Aluminum | 17.32 % | Al | 32.73 % | Al2O3 | |
| Silicon | 18.03 % | Si | 38.57 % | SiO2 | |
| Carbon | 1.28 % | C | 4.71 % | CO2 | |
| Oxygen | 46.22 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Tetragonal – Dipyramidal |
| Crystal Habit: | Crystals prismatic, typically with flat pyramidal terminations, striated || [001], to 0.7 m; granular, massive. |
| Twinning: | None |
| Cleavage: | Distinct on {100}{110} |
| Fracture: | Irregular/Uneven, Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.0 – 6.0 |
| Density: | 2.74 – 2.78 (g/cm3) |
| Luminescence: | Commonly orange to bright yellow to red under SW and LW UV light. |
| Radioactivity: | Not Radioactive |
| Color: | Colorless, white, grey; pink, violet, blue, yellow, orange-brown, brown; colorless in thin section. |
| Transparency: | Transparent to opaque |
| Luster: | Vitreous to pearly or resinous. |
| Refractive Index: | 1.590 – 1.600 Uniaxial ( – ) |
| Birefringence: | 0.034 – 0.038 |
| Dispersion: | n/a |
| Pleochroism: | None |
