| Periclase | |
|---|---|
 White to light greenish periclase with blacksrebrodolskite fromRonneburg, Thuringia, Germany (Picture size 5 mm) | |
| General | |
| Category | Oxide minerals |
| Formula | MgO |
| IMA symbol | Per[1] |
| Strunz classification | 4.AB.25 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m3 2/m) |
| Space group | Fm3m |
| Unit cell | 4.21 Å; Z = 4 |
| Identification | |
| Color | Colorless, grayish white, yellow, brownish yellow, green, black |
| Crystal habit | Granular, generally occurs as anhedral to subhedral octahedral crystals in matrix |
| Cleavage | {001} perfect; {111} imperfect, may exhibit parting on{011} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.56–3.68 (meas.) 3.58 (calc.) |
| Optical properties | Isotropic |
| Refractive index | n = 1.735–1.745 |
| Other characteristics | Fluorescent, long UV=light yellow. |
| References | [2][3][4][5] |
Periclase is amagnesium mineral that occurs naturally incontactmetamorphic rocks and is a major component of most basicrefractory bricks. It is acubic form ofmagnesium oxide (MgO). In nature it usually forms asolid solution withwüstite (FeO) and is then referred to asferropericlase or magnesiowüstite.[6]
It was first described in 1840 and named from the Greek περικλάω (to break around) in allusion to its cleavage. Thetype locality isMonte Somma, Somma-Vesuvius Complex,Naples Province,Campania,Italy.[5]
The old term for the mineral ismagnesia. Stones from theMagnesia region in ancientAnatolia contained both magnesium oxide and hydratedmagnesium carbonate as well asiron oxides (such asmagnetite). Thus these stones, calledStones from Magnesia in antiquity, with their unusual magnetic properties were the reason the termsmagnet andmagnetism were coined.
Periclase is usually found inmarble produced bymetamorphism ofdolomiticlimestones. It readily alters tobrucite under near surface conditions.[5]
In addition to its type locality, it is reported fromPredazzo,Trentino,Italy;Carlingford, County Louth, Ireland;Broadford, Skye and the island ofMuck, Scotland;León, Spain; theBellerberg Volcano,Eifel district, Germany;Nordmark andLångban,Varmland,Sweden; andKopeysk, southernUral Mountains, Russia. In the US it occurs at the Crestmore quarry,Riverside County, California;Tombstone, Arizona;Gabbs district,Nye County, Nevada. InCanada, it occurs atOka,Quebec and inAustralia, west ofCowell,Eyre Peninsula,South Australia.[3]
Thecrystal structure of periclase corresponds to that ofhalite and has been studied extensively due to its simplicity. As a consequence, the physical properties of periclase are well known, which makes the mineral a popular standard in experimental work. The mineral has been shown to remain stable at pressures up to at least 360 GPa.[7]
Ferropericlase(Mg,Fe)O makes up about 20% of the volume of thelower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicateperovskite(Mg,Fe)SiO3; it also is the major host for iron in the lower mantle.[8][9] At the bottom of thetransition zone of the mantle, the reaction
transformsγ-olivine into a mixture of perovskite and ferropericlase andvice versa. In the literature, this mineral phase of the lower mantle is also often calledmagnesiowüstite.[6]