Lava Rock with Secondary Mineral Crusts
Basalt (with possible Calcite or Zeolite crusts) · Mineral Specimen / Igneous Rock
Crystal System
Amorphous to Microcrystalline matrix with various habits in secondary crusts (likely Trigonal or Orthorhombic)
Mineral Group
Silicates (Mafic igneous rock) with secondary Carbonates or Silicates
Chemical Formula
Complexity of silicates (Na, Ca)(Mg, Fe, Al)Si2O6 (Pyroxene) + CaAl2Si2O8 (Plagioclase) + (Fe,Mg)2SiO4 (Olivine)
Formation Process
Igneous (Extrusive); cooling of mafic lava on the earth's surface. Secondary white crusts form via hydrothermal precipitation or weathering
About This Crystal
An opaque, dark grey to black fine-grained volcanic matrix. Surface is rough and vesicular. Features white to pale pink secondary mineral crusts or 'vugs' coating the darker host rock, displaying a dull to earthy luster
Physical Characteristics
Body color: Dark grey/Black with white crusts; Streak: Grey to white; Cleavage: None (rock); Fracture: Irregular/sub-conchoidal; Specific Gravity: 2.8-3.0; Non-fluorescent usually
Optical Properties
Opaque; No visible pleochroism or dispersion; Luster is primarily earthy to vitreous in small crystal pockets
Hardness & Durability
Origin Region
Volcanic regions such as Hawaii, Iceland, or the Deccan Traps; found in basaltic flow environments
Hardness & Durability
Mohs hardness: 5-6 (basalt matrix); Crusts range from 3 (Calcite) to 5 (Zeolites). Generally durable but prone to surface abrasion
Care & Maintenance
Wash with warm soapy water and a soft brush; avoid acidic cleaners if the white crust is calcite, as it will dissolve; keep dry to prevent further weathering
Rarity & Value
Common; Value is low for raw specimens, primarily used for landscaping or geological study; higher if specific rare zeolite crystals are present
Special Characteristics
Vesicular texture (bubbles from gas escaping during cooling); secondary mineral mineralization filling cavities (amygdules)
Lore & History
Historically used as building material and grinding stones in ancient cultures; traditionally associated with grounding and rebirth due to its origin from the earth's core