Amygdaloidal Basalt
Amygdaloidal Basalt (with Quartz and Calcite infilling) · Mineral Specimen / Igneous Rock
Crystal System
Amorphous to Microcrystalline matrix; Orthorhombic/Trigonal secondary crystals
Mineral Group
Silicates (Matrix) / Oxides and Carbonates (Infillings)
Chemical Formula
Complex Silicate (Matrix: CaAl2Si2O8 + (Mg,Fe)2SiO4; Infillings: SiO2 / CaCO3)
Formation Process
Igneous: Volcanic gas bubbles (vesicles) in cooling lava are later filled with secondary minerals from hydrothermal fluids.
About This Crystal
A dark, fine-grained volcanic matrix featuring white to cream-colored amygdules. The surface is rounded by water erosion, showing a dull to sub-vitreous luster.
Physical Characteristics
Color: Dark grey/black matrix with white spots; Streak: White to Grey; Fracture: Conchoidal to uneven; Specific Gravity: 2.8 - 3.0.
Optical Properties
Matrix is opaque; mineral infills (amygdules) are translucent to opaque with low birefringence depending on the mineral species.
Hardness & Durability
Origin Region
Notable sources include Lake Superior (USA), India (Deccan Traps), and Iceland; found in volcanic fields worldwide.
Hardness & Durability
Matrix: 5-6 (Mohs); Mineral infills: 3 (Calcite) to 7 (Quartz); Variable durability due to composite nature.
Care & Maintenance
Clean with warm soapy water; avoid harsh acids (like vinegar) which may dissolve calcite infill; store away from harder stones.
Rarity & Value
Common; primarily valued as educational geological specimens or local pocket stones; low commercial gem value.
Special Characteristics
Amygdaloidal texture (almond-shaped inclusions representing prehistoric gas bubbles); may show faint fluorescence if calcite is present.
Lore & History
Historically used in road construction and as a material for primitive tools; traditionally viewed as a stone of 'grounding' and 'stability' in folk lore.