“Magnesium Oxide (Periclase),” synthetic, doped with nickel, ~ 5 carats. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Periclase has been synthesized in large masses in the laboratory, but these have no market significance. A faceted natural periclase would be a great rarity due to the extreme scarcity of suitable faceting rough. The expected size would be less than 1 carat.
| Data | Value |
|---|---|
| Name | Periclase |
| Crystallography | Isometric. Crystals octahedral, cubic; commonly as rounded grains. |
| Refractive Index | 1.736 |
| Colors | Colorless, white, gray, yellow, brownish yellow, green, black. |
| Luster | Vitreous. |
| Hardness | 5.5 |
| Fracture | Uneven |
| Specific Gravity | 3.56. |
| Birefringence | None. |
| Cleavage | Perfect 1 direction |
| Stone Sizes | I have not seen any faceted gems, but if such gems existed, they would be very small. Transparent grains from Vesuvius might be cuttable, but in general periclase is not known in transparent. large crystals. |
| Luminescence | Pale yellow in LW (Terlingua, Texas). |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long |
| Transparency | Transparent. |
| Formula | MgO |
| Pleochroism | None. |
| Optics | Isotropic; N = 1.736. |
Optics: Isotropic; N: 1.736.
Occurrence: Occurs in marbles, due to high-temperature contact metamorphism.
Texas; New Mexico.
Spain; Sardinia; Czech Republic; Slovakia.
Crestmore, Riverside County, California: embedded grains.
Vesuvius, Italy: as glassy grains in the lava rocks.
Nordmark, Sweden: in the Mn mines.
Comments: Periclase has been synthesized in large masses in the laboratory, but these have no market significance. A faceted natural periclase would be a great rarity due to the extreme scarcity of suitable faceting rough. The expected size would be less than 1 carat.
Name: From the Greek peri plus klastos, to break around, in allusion to the cleavage.
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