Periclase is a high-temperature magnesium oxide mineral typically found in metamorphosed carbonate rocks or volcanic ejecta. It is known for its perfect cubic cleavage and vitreous luster, though natural specimens are often altered to brucite due to hydration upon exposure to atmospheric moisture.
Is this periclase?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch periclase with a known reference. Periclase sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, brownish yellow, green, gray white, yellow.
- 5Look at form & habitCrystal system: cubic. Typical habit: granular.
Often confused with
Periclase vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Periclase is noticeably harder (Mohs 5.5 vs. 4).
How to tell apart: Periclase is noticeably harder (Mohs 5.5 vs. 2-2.5).
How to tell apart: Periclase is noticeably harder (Mohs 5.5 vs. 2.5-2.75); streak differs, so Periclase leaves white, Galena leaves lead-gray; luster reads vitreous on Periclase and metallic on Galena.
Often found alongside periclase
Minerals reported to co-occur with periclase. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgO
- Mohs hardness
- 5.5
- Density
- 3.56-3.68 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Cubic
- Crystal habit
- Granular
- Cleavage
- {001}, perfect; on {111}, good; may exhibit parting on {011}
- Rarity
- Rare
- Uses
- Collector, Refractory materials
- Host rock
- A product of the high-temperature metamorphism of magnesian limestones and dolostone
Where rockhounds find periclase
Classic worldwide localities
- Crestmore quarry, Riverside Co., California, USA
- Tombstone, Cochise Co., Arizona, USA
- Gabbs mine, Gabbs district, Nye Co., Nevada, USA
- Monte Somma, Campania, Italy
- Predazzo, Tirol, Austria
- Carlingford, Co. Louth, Ireland
Field-hunting tip
Where it forms: A product of the high-temperature metamorphism of magnesian limestones and dolostone. If you start seeing forsterite, magnesite, brucite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify periclase?+
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What rocks look like periclase?+
What minerals are found with periclase?+
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Find periclase on the map
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