Bytownite (Feldspar)
Bytownite is a variety of Anorthite and it is an associate that is rare of Plagioclase Series of the Feldspar number of minerals that features Albite, Amazonite, Andesine, Anorthite, Bytownite, Hyalophane, Labradorite, Moonstone, Oligoclase, Orthoclase, Sanidine, and Sunstone. Bytownite is a bright and gorgeous champagne gem that is colored. Most gem quality Bytownite crystals are currently coming from Chihuahua, Mexico and Grants District, New Mexico.
Bytownite is one of the less frequently identified feldspars, although nevertheless quite typical. The “type material” from Ottawa, Ontario, Canada was later shown to be a combination. Somewhere else in Canada, from the Shawmere anorthosite, Foleyet Township, Ontario, as well as on Yamaska Mountain, near Abbotsford, Quebec. On Rhum Island, Scotland. At Eycott Hill, near Keswick, Cumberland, England. From Närödal, Norway. In Greenland, from Fiskenaesset and Storo. In the Bushveld complex, Transvaal, South Africa. In the USA, in the Stillwater complex, Montana; from Cornwall, Lebanon County, and Phoenixville, Chester County, Pennsylvania; near Lakeview, Lake County, Oregon; into the Cuss that is fortunate mine Tombstone, Cochise County, Arizona; and from the Grants district, McKinley County, New Mexico. From Isa Valley, Western Australia.
| Category: | Plagioclase Feldspar |
| Chemical Formula: | (Ca,Na)(Si,Al)4O8 |
| Calcium Sodium Aluminum Silicate | |
| Molecular Weight: | 275.01 gm |
| Composition: | Sodium | 1.67 % | Na | 2.25 % | Na2O |
| Calcium | 11.66 % | Ca | 16.31 % | CaO | |
| Aluminum | 17.66 % | Al | 33.37 % | Al2O3 | |
| Silicon | 22.47 % | Si | 48.07 % | SiO2 | |
| Oxygen | 46.54 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Triclinic – Pinacoidal |
| Crystal Habit: | Crystals are rare; flattened, to 3 cm; commonly as cleavable masses or anhedral grains in massive aggregates. |
| Twinning: | Common after the Albite, Carlsbad, and Pericline laws, developed in simple to complex combinations. |
| Color: | Colorless, White, Gray, Pale Yellow |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous, Pearly on cleavages |
| Refractive Index: | 1.563 – 1.585 Biaxial ( – ) |
| Specific gravity: | 2.72 – 2.74 |
| Birefringence: | 0.0100 – 0.0110 |
| Fracture: | Uneven to conchoidal |
| Dispersion: | r > v, strong (mindat.org) r < v, weak (Handbook of Mineralogy pdf) |
| Birefringence: | δ = 0.010 – 0.011 |
| Pleochroism: | None |
