igneous
Quartz crystals on Basalt
SiO2 (Quartz) on Mafic Igneous Rock (Basalt)
Hardness: 7 (Quartz), 5-6 (Basalt host); Color: Colorless to white crystals on a dark grey/black matrix; Luster: Vitreous (crystals) to dull (host); Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture)
- Hardness
- 7 (Quartz), 5-6 (Basalt host)
- Color
- Colorless to white crystals on a dark grey/black matrix
- Luster
- Vitreous (crystals) to dull (host)
Identified More igneous →
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Physical properties
Hardness: 7 (Quartz), 5-6 (Basalt host); Color: Colorless to white crystals on a dark grey/black matrix; Luster: Vitreous (crystals) to dull (host); Crystal Structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed via hydrothermal precipitation where silica-rich fluids filled vesicles or cracks in basaltic lava flows. The basalt formed from cooling lava, while the quartz crystals grew later as mineral-rich water permeated the rock.
Uses & applications
Geological collecting, educational specimens, and small-scale ornamental pieces. Basalt itself is heavily used in construction as aggregate.
Geological facts
Basalt is the most common volcanic rock on Earth and makes up most of the ocean floor. Small quartz druses like this are frequently found in gas bubbles known as amygdules.
Field identification & locations
Identified by the contrast between the dark, fine-grained host rock and the hard, glassy crystals that can scratch glass. Common in volcanic terrains such as the Pacific Northwest, India (Deccan Traps), or Iceland.
