igneous
Quartz-veined Diabase or Basalt Pebble
Diabase or Basalt with Hydrothermal Quartz Veins (SiO2)
Hardness: 6-7 on Mohs scale (due to quartz veins), 5-6 for the host rock; Color: Dark grey to greenish-black host with stark white quartz veins; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to cryptocrystalline host with macrocrystalline quartz in the veins; Specific gravity: ~2.8-3.0
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale (due to quartz veins), 5-6 for the host rock; Color: Dark grey to greenish-black host with stark white quartz veins; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline to cryptocrystalline host with macrocrystalline quartz in the veins; Specific gravity: ~2.8-3.0
Formation & geological history
Formed via volcanic or hypabyssal intrusive activity where a mafic host rock (like diabase or basalt) cooled, fractured, and was subsequently permeated by hydrothermal silica-rich fluids that crystallized into quartz veins.
Uses & applications
Primarily collected as a decorative specimen or a natural curiosity due to the striking contrast of the white veins against the dark host rock.
Geological facts
These rocks are often called 'Wishing Rocks' or 'Lucky Rocks' in regions like the Great Lakes or Pacific Northwest. The white lines are mineral veins formed when silica-bearing water fills cracks deep within the Earth's crust and solidifies.
Field identification & locations
Easily identified by the stark white mineral veins (usually quartz or calcite) intersecting a dark, weathered igneous pebble. Found commonly in glacial tills, riverbeds, and beaches worldwide.
