Hardystonite
Hardystonite is a calcium zinc silicate mineral that is usually a dull, unattractive white color in natural daylight but will fluoresce purple under short-wave (SW) ultraviolet (UV) light and blue to violet blue under logn-wave (LW) ultraviolet (UV) light. For this reason Hardystonite is well known to collectors of fluorescent minerals from Franklin and Sterling Hill, New Jersey. Fluorescence occurs when the ultraviolet light (invisible to humans) imparts energy to some of the atoms in the mineral. This energy is converted by the atom into visible light that we can then see.
Hardystonite is often found in association with other fluorescent minerals such as Calcite, Clinoherderite, Esperite, Fluorite, Willemite and Wollastonite. When two or more of these minerals are found together in one specimen it can make for wonderfully colorful fluorescent specimens. The purple or violet-blue color of Hardystonite really stands out among these minerals.
Distribution: From the type locality at Franklin Mine, Sussex County, New Jersey, USA. At Vrchlice River valley, Policany, Kutna Hora, Central Bohemian Region, Czech Republic. At Gottesbelohnung smelter, Hettstedt, Mansfeld Basin, Saxony-Anhalt, German. At Tsumeb, Otjikoto Region, Namibia. At Swietochlowice, Katowice, Upper Silesia (Slaskie), Poland.
| Category: | Sorosilicates |
| Chemical Formula: | Ca2ZnSi2O7 |
| Calcium Zinc Silicate | |
| Molecular Weight: | 313.71 gm |
| Composition: | Calcium | 25.55 % | Ca | 35.75 % | CaO |
| Zinc | 20.84 % | Zn | 25.94 % | ZnO | |
| Silicon | 17.91 % | Si | 38.31 % | SiO2 | |
| Oxygen | 35.70 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Tetragonal – Scalenohedral |
| Crystal Habit: | In coarse, columnar masses; granular and as isolated grains. |
| Twinning: | None |
| Cleavage: | Good on {001}, Poor on {100} and {110} |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 3.0 – 4.0 |
| Density: | 3.396 – 3.443 (g/cm3) |
| Luminescence: | Fluorescent; dull to dark purple under SW UV, blue to violet blue under LW UV |
| Radioactivity: | Not Radioactive |
| Color: | White, pale pinkish, light brownish white, grayish white; colorless in thin section. |
| Transparency: | Translucent |
| Luster: | Vitreous, Resinous, Dull |
| Refractive Index: | 1.657 – 1.672 Uniaxial ( – ) |
| Birefringence: | 0.011 |
| Dispersion: | n/a |
