Periclase Mineral Overview
- Mineral name: Periclase
- Mineral class: Oxide
- Chemical formula: MgO (magnesium oxide)
- Crystal system: Isometric (cubic)
- Mohs hardness: 5.5–6
- Color range: Colorless, white, gray, yellowish, greenish, black (when impure)
- Luster: Vitreous to dull
- Streak: White
- Cleavage: Perfect (cubic)
- Fracture: Conchoidal to uneven
- Specific gravity: Approximately 3.5–3.6
- Transparency: Transparent to opaque
- Common locations: Italy, United States, Russia, Canada
- Uses: Refractory materials, industrial magnesium source
- Similar minerals: Halite, spinel, brucite
Naming and Classification
Periclase is a magnesium oxide mineral, one of the simplest oxide minerals in terms of chemical composition.
The name comes from the Greek periklasis, meaning “breaking all around,” referring to its perfect cubic cleavage.
It is the natural mineral form of magnesium oxide (MgO), a compound widely used in industrial applications.
Physical and Optical Characteristics
Periclase typically occurs as:
- Cubic crystals
- Granular masses
- Disseminated grains within host rock
Well-formed crystals are relatively rare.
It is usually colorless to white, but impurities (especially iron) can produce:
- Yellowish
- Greenish
- Dark gray to black colors
The luster is vitreous on fresh surfaces but may appear dull in massive forms. With a Mohs hardness of 5.5 to 6, it is moderately hard.
It exhibits perfect cubic cleavage, similar to halite, but is harder and denser.
Chemical Composition and Structure
Periclase is composed of:
- Magnesium (Mg)
- Oxygen (O)
Its structure is:
- Cubic lattice, similar to halite (NaCl structure type)
This simple structure contributes to:
- Its cleavage
- Its relatively high stability at high temperatures
Formation and Geological Occurrence
Periclase forms in high-temperature environments, particularly in:
Metamorphic Rocks
- Formed from the metamorphism of magnesium-rich limestones or dolomites
- Occurs in contact metamorphic zones
Igneous and Mantle Environments
- Found in ultramafic rocks
- Can form under extreme الحرارة and pressure
Typical formation conditions include:
- High temperatures
- Low water availability (it readily alters in the presence of water)
It is commonly associated with:
- Brucite (forms from hydration of periclase)
- Spinel
- Forsterite (olivine)
Alteration (Important Property)
Periclase is unstable in the presence of water and readily alters to:
- Brucite (Mg(OH)₂)
This hydration process is common and often limits the preservation of pure periclase in natural environments.
Common Locations
Periclase is found in several notable regions:
- Italy: Classic metamorphic localities
- United States: California and New York
- Russia and Canada: Metamorphic terrains
It is often found in high-temperature metamorphic rocks.
Uses and Practical Significance
While natural periclase is relatively rare, its synthetic equivalent is extremely important:
Industrial Applications
- Refractory materials (furnace linings)
- Heat-resistant bricks
- Crucibles
Magnesium Source
- Used in producing magnesium compounds
Scientific Importance
- Studied in high-temperature geology and mantle processes
Similar and Related Minerals
Periclase can resemble:
- Halite: Softer and soluble in water
- Spinel: Harder and lacks perfect cleavage
- Brucite: Softer and formed from alteration
Hardness and reactivity with water help distinguish periclase.
Identification Notes for Collectors
- Look for cubic crystals in high-temperature metamorphic rocks
- Note moderate hardness (5.5–6)
- Observe perfect cubic cleavage
- Consider association with magnesium-rich environments
- Check for alteration to brucite
Periclase is a magnesium oxide mineral, recognized for its simple composition, cubic structure, and formation in high-temperature environments, and is especially important as the natural counterpart to industrial magnesium oxide.