Norbergite
Norbergite is a rare member of the Humite Group of minerals that includes Chondrodite, Clinohumite, Humite and Norbergite. The chemical formula of Norbergite is Mg3(SiO4) (F, OH)2 (Magnesium Silicate Fluoride Hydroxide) and its molecular weight is 202.00 gm. It is one of several rare minerals that have been found at the famous mines at Franklin, New Jersey, USA. It is also one of the many fluorescent minerals found there. It will glow tan to canary-yellow under SW UV. It is often found associated with other fluorescing minerals such as red fluorescing Calcite and blue fluorescing Diopside. The combination of different fluorescing colors can be quite attractive. The hardness is 6.0 – 6.5 and the specific gravity 3.177 (g/cm3). Norbergite rarely forms transparent crystals but mostly as tiny translucent to opaque crystals or granular masses. Therefore, Norbergite is only suitable for cabochons.
There are only a few locations for finding Norbergite, at the Type Locality of Östanmoss mine, Norberg, Västmanland, Sweden; Mogok, Sagaing District, Mandalay Division, Burma (Myanmar); San Vito quarry, San Vito, Ercolano, Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy; Near Loch Ness, Inverness-shire, Scotland, in the USA at Franklin, Franklin Mining District, Sussex County, New Jersey; Limecrest Quarry, Sparta Township, Sussex Co., New Jersey.
| Category: | Nesosilicates |
| Chemical Formula: | Mg3(SiO4) (F, OH)2 |
| Magnesium Silicate Fluoride Hydroxide | |
| Molecular Weight: | 202.00 gm |
| Composition: | Magnesium | 36.10 % | Mg | 59.86 % | MgO |
| Silicon | 13.90 % | Si | 29.74 % | SiO2 | |
| Hydrogen | 0.25 % | H | 2.23 % | H2O | |
| Oxygen | 35.64 % | O | |||
| Fluorine | 14.11 % | F | 14.11 % | F | |
| – | – % | F | -5.94 % | -O=F2 | |
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Crystals rare, to 2.5 cm, thick tabular, typically rounded and highly modified; granular. |
| Twinning: | None |
| Cleavage: | [???] Distinct |
| Fracture: | Irregular/Uneven to Sub-Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.0 – 6.5 |
| Density: | 3.177 (g/cm3) |
| Luminescence: | May fluoresce tan-yellow to canary-yellow under SW UV light. |
| Radioactivity: | Not Radioactive |
| Color: | Tan, Yellow, Yellow-Orange, Orange-Brown, Pink with Purplish tint, White; pale Yellow to Colorless in thin section |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous to Resinous |
| Refractive Index: | 1.563 – 1.593 Biaxial ( + ) |
| Birefringence: | 0.0270 |
| Dispersion: | Slight to Strong; r > v |
| Pleochroism: | X = pale yellow; Y = very pale yellow; Z = colorless |
