Hessonite
Hessonite may be the more variety that is typical of Garnet which is a member of the Garnet number of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. Other kinds of Grossular Garnet are Hessonite, Rosolite and Tsavorite. Hessonite is named from the Greek word “hesson” meaning “inferior”, because of its hardness that is inferior to varieties of Garnet. Hessonite Garnets range in color from cinnamon-brown to orange and have been called “Cinnamon Garnet” as a result of its color. The color is because of the addition of iron to its chemical formula. Gem quality Hessonite is located in Sri Lanka, Tanzania, Brazil and California, USA.
Grossular, also known as Grossularite, is really a calcium aluminum variety of the Garnet Group. The name Grossular comes from the name that is botanical the gooseberry, Ribes Grossularium, in guide to the green number of Garnet that was initially found in the Vilyui River Basin, Eastern-Siberian Region, Russia. Hessonite, the genuine name Garnet comes through the Latin word granatus meaning grain. This is from the contrast of garnet grains in rock looking like the dark red seeds regarding the Pomegranite fruit scattered on the ground. Tsavorite, Rosolite and Viluite are kinds of Grossular and are not recognized as distinct mineral species.
| Chemical Formula: | Ca3Al2(SiO4)3 + Fe |
| Calcium Aluminum Iron Silicate | |
| Molecular Weight: | 450.45 gm |
| Composition: | Calcium | 26.69 % | Ca | 37.35 % | CaO |
| (Grossular) | Aluminum | 11.98 % | Al | 22.64 % | Al2O3 |
| Silicon | 18.71 % | Si | 40.02 % | SiO2 | |
| Oxygen | 42.62 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Isometric – Hexoctahedral |
| Crystal Habit: | Commonly in dodecahedra or trapezohedra, up to 15 cm, with striated faces. Also granular, compact, and massive. |
| Twinning: | None observed |
| Cleavage: | None observed. Parting rarely observed on {110}. |
| Fracture: | Irregular/Uneven, Sub-Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.5 – 7.0 |
| Density: | 3.594 (g/cm3) |
| Luminescence: | Almost always non-fluorescent; may be a weak golden yellow under LW & SW UV. |
| Radioactivity: | Not Radioactive |
| Color: | Yellow-Green, pale to dark Green; golden Yellow, Pink, Red, Orange, Brownish Red, Yellowish Brown; Colorless, White, Gray, Black; may be sectored: Colorless in thin section. |
| Transparency: | Transparent to Opaque |
| Luster: | Vitreous, Sub-Vitreous, Resinous |
| Refractive Index: | 1.731 – 1.754 Isotropic. RI increases with increasing iron contents (usually Fe3+). |
| Birefringence: | 0.000 (Isotropic); may have weak strain birefringence of 0.0 – 0.005 |
| Dispersion: | Strong |
| Pleochroism: | None |
