Plagioclase is a sub-series of the feldspar group. Members of the series include labradorite, oligoclase, and albite, defined by their albite and anorthite content. The highest concentration of albite is found in the albite member of the series.
Labradorite is the most commonly used gem material from this series. Play-of-color exhibited by labradorite makes this gem popular for carving as well as for cabochons and slabs.
Gemological Information for Plagioclase
| Color: | Gray to Black for Labradorite, Yellow, Orange to Brown for Oligolcase |
| Crystal Structure: | Monoclinic |
| Refractive Index: | 1.599 to 1.568 Plagioclase |
| Durability: | Poor |
| Hardness: | 6 to 6.5 |
| Family: | Feldspar |
| Similar Stones: | Beryl, Quartz, Scapolite, Goldstone Glass |
| Treatments: | Wax Impregnation, Irradiation |
| Country of Origin: | Brazil, Madagascar, Norway, US, Russia |
Plagioclase Care
| Ultrasonic Cleaning: | Never |
| Steam Cleaning: | Never |
| Warm Soapy Water: | Safe |
| Chemical Attack: | Hydrofluoric Acid attacks quickly. Impurities may react to other acids. |
| Light Sensitivity: | Stable |
| Heat Sensitivity: | Can Crack, Fade and Cleave |
Sources
- Gem Reference Guide, Los Angeles: Gemological Institute of America, 1988. Pp. 101-107.
- Hall, Cally. Gemstones, Smithsonian Handbooks. London, DK Penguin Random House, 2021.
- Newman, Harold. An Illustrated Dictionary of Jewelry, New York: Thames and Hudson, 1981. Pp. 122.
- Schumann, Walter. Gemstones of the World, New York: Sterling Publishing, Co., 1977. Pp. 164-167.