igneous
Basalt with Plagioclase or Quartz Inclusion
Melanocratic Basalt with Porphyritic Inclusion
Hardness: 6 (matrix); Color: Dark grey to charcoal with a yellowish-white inclusion; Luster: Dull/Earthy (water-worn); Texture: Fine-grained/Aphanitic matrix; Specific Gravity: 2.8-3.0
- Hardness
- 6 (matrix)
- Color
- Dark grey to charcoal with a yellowish-white inclusion
- Luster
- Dull/Earthy (water-worn)
Identified More igneous →
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Physical properties
Hardness: 6 (matrix); Color: Dark grey to charcoal with a yellowish-white inclusion; Luster: Dull/Earthy (water-worn); Texture: Fine-grained/Aphanitic matrix; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The visible inclusion likely formed as a larger crystal (phenocryst) or a small secondary mineral filling a vesicle (amygdule) during or after the volcanic eruption.
Uses & applications
Extensively used in construction for road base, concrete aggregate, and railroad ballast. Small water-worn pebbles like this are used in decorative landscaping and as aquarium substrate.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Commonly found on beaches, riverbeds, and in volcanic fields. Identified by its dark, dense matrix and rounded, smooth texture from water erosion. The light spot is a distinct mineral pocket within the darker volcanic glass/ash mixture.
