Antigorite
Antigorite was named in 1840 by Mathias Eduard Schweizer for the sort locality, Valle di Antigorio, Domodossola, Piedmont, Italy; even though there is some question whether it had been found regarding the side that is italian the Swiss side for the edge. Antigorite is a known member of the Serpentine Group of minerals that also includes Chrysotile and Lizardite. The Serpentine Group is just a subgroup of the Kaolinite-Serpentine Group. Most Antigorite is opaque and fibrous but a couple of places produce beautiful, translucent, pale to dark material that is green for cabochons, carvings and rarely faceted gems.
There are a few of gem types of Antigorite; Bowenite and Williamsite. Bowenite is a translucent, light green to dark green, rarely blue-green, variety. Bowenite from China is light and translucent yellowish green while Bowenite from brand new Zealand are dark green. Bowenite was known as by James D. Dana in 1850 for George T. Bowen, who first analyzed the mineral from Rhode Island in 1822.
Williamsite is really a very translucent, medium to deep, apple variety that is green of that gets its color from the existence of chromium (Cr). It often has inclusions of black specks and microcrystals of Chromite in it. Williamsite originally came from the State that is historic Line Mine which lies just inside Lancaster County, Pennsylvania regarding the Pennsylvania-Maryland border. Williamsite had been named by Charles Upham Shepard in 1848 in honor of its discoverer, Lewis White Williams (1804-1873), a geologist and mineralogist of western Chester, Chester County, Pennsylvania.
Sources of Antigorite are the type locality; Antigorio Valley, Piedmont, Italy; New South Wales, Australia; Tirol Austria; Liaoning Province, China; Nagasaki and Fukuoka Prefectures, Japan; Glen Urquhart, Scotland; plus in the united states at Texas, Pennsylvania; Baltimore, Maryland; and Brewster, New York. The majority of these locations produce opaque, fibrous material perhaps not suitable for faceted gems or cabochons.
| Chemical Formula: | (Mg;Fe2+)3Si2O5(OH)4 |
| Magnesium Iron Silicate Hydroxide | |
| Molecular Weight: | 300.77 gm |
| Composition: | Magnesium | 18.18 % | Mg | 30.15 % | MgO |
| Iron | 13.93 % | Fe | 17.92 % | FeO | |
| Silicon | 18.68 % | Si | 39.95 % | SiO2 | |
| Hydrogen | 1.34 % | H | 11.98 % | H2O | |
| Oxygen | 47.88 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Domatic |
| Crystal Habit: | Minute crystals, typically platy along [001], rarely elongated along [010]; some plates have rectangular outline due to cleavage; commonly bladed or fibrous. |
| Twinning: | May exhibit two- or three-fold twins rotated 60° about an axis [001]. |
| Cleavage: | Perfect on {001}, observed on {100} and {010} |
| Fracture: | Conchoidal or Splintery |
| Tenacity: | Brittle |
| Moh’s Hardness: | 3.5 – 4.0 |
| Density: | 2.50 – 2.60 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Green, Blue-Green, White; Colorless to pale Green in thin section. |
| Transparency: | Translucent to Sub-Opaque |
| Luster: | Resinous, Greasy, Silky, Waxy, Earthy |
| Refractive Index: | 1.555 – 1.573 Biaxial ( – ) |
| Birefringence: | 0.005 – 0.006 |
| Dispersion: | Weak; r > v |
| Pleochroism: | None |
