igneous
Vesicular Basalt with Zeolite
Mafic volcanic rock with Hydrated Aluminosilicate minerals (Zeolite group)
Hardness: 5-6 (Basalt) / 3-5 (Zeolites); Color: Dark grey to black matrix with white or clear crystals; Luster: Dull (matrix) to Vitreous (crystals); Crystal structure: Amorphous/fine-grained matrix with monoclinic or orthorhombic crystalline inclusions; Cleavage: None in basalt, varies in zeolites.
- Hardness
- 5-6 (Basalt) / 3-5 (Zeolites)
- Color
- Dark grey to black matrix with white or clear crystals
- Luster
- Dull (matrix) to Vitreous (crystals)
Identified More igneous →
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Physical properties
Hardness: 5-6 (Basalt) / 3-5 (Zeolites); Color: Dark grey to black matrix with white or clear crystals; Luster: Dull (matrix) to Vitreous (crystals); Crystal structure: Amorphous/fine-grained matrix with monoclinic or orthorhombic crystalline inclusions; Cleavage: None in basalt, varies in zeolites.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The white crystals (zeolites) formed later as low-grade metamorphic or hydrothermal minerals filling the gas bubbles (vesicles) left by trapped volcanic gases.
Uses & applications
Basalt is used heavily in construction as aggregate and road base. Zeolites are prized by collectors and used industrially as molecular sieves, in water purification, and as catalysts.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The presence of zeolites indicates that after the lava cooled, it was exposed to warm, mineral-rich groundwater.
Field identification & locations
Identify in the field by the dark, heavy, fine-grained matrix with 'pockmarks' or holes filled with white crystalline minerals. Commonly found in volcanic regions like the Pacific Northwest, Iceland, and India's Deccan Traps. Collectors should look for undamaged crystal faces in the cavities.
