Vesicular Basalt with Coralline Algae Encrustation
Basalt (Mafic Extrusive Igneous Rock) with Lithothamnion species · Mineral Specimen / Igneous Rock / Marine Geological Sample
Crystal System
Amorphous to Microcrystalline (Aphanitic texture); encrustation is Trigonal (Calcite-based)
Mineral Group
Silicates (Pyroxene and Plagioclase Feldspar groups); Encrustation is Carbonate
Chemical Formula
Complex Silicate (primarily [Ca,Na][Mg,Fe,Al]Si2O6 + (Na,Ca)(Si,Al)4O8) with CaCO3 overgrowth
Formation Process
Igneous (extrusive volcanic flow cooling rapidly) with subsequent Biogenic (marine organism growth) encrustation
About This Crystal
A dark charcoal to black vesicular volcanic rock. The surface is porous with gas bubbles (vesicles) and is heavily encrusted with pinkish-red and white calcified marine algae and bryozoans.
Physical Characteristics
Color: Black host rock with pink/white spots; Streak: Grey to greenish; Cleavage: None; Fracture: Uneven/Scoriaceous; Specific Gravity: 2.8 - 3.0; Luster: Dull to earthy
Optical Properties
Opaque; Non-refractive in hand specimen; No pleochroism or dispersion visible; Dull light absorption due to porosity
Hardness & Durability
Origin Region
Coastal volcanic regions such as Hawaii, Iceland, or the Mediterranean; found in intertidal zones
Hardness & Durability
Mohs 5 to 6 for basalt host; Encrustation is soft (Mohs 3); Toughness is high for the rock, brittle for the pink crust
Care & Maintenance
Dust gently; Avoid acids (vinegar will dissolve the pink crust); Keep dry to prevent salt crystallization; Fragile surface growths
Rarity & Value
Common; Value is low (educational or decorative); Higher value if it contains rare xenoliths or olivine crystals
Special Characteristics
Vesicular texture (pitted surface); Coralline algae encrustation (pink patches) indicating it was submerged in seawater
Lore & History
Used historically as a building material (pavers); Metaphysically associated with grounding and the root chakra due to its volcanic origins