igneous
Vein-filled Basalt or Diabase Pebble
Mafic igneous rock with quartz/calcite veins
Hardness of 6-7 (due to quartz veins) or 5-6 for the host rock, dark grey to black color with contrasting white to yellowish mineral veins (likely quartz or epidote), vitreous to dull luster, dense and compact crystal structure with conchoidal to uneven fracture.
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Physical properties
Hardness of 6-7 (due to quartz veins) or 5-6 for the host rock, dark grey to black color with contrasting white to yellowish mineral veins (likely quartz or epidote), vitreous to dull luster, dense and compact crystal structure with conchoidal to uneven fracture.
Formation & geological history
Formed from cooling mafic magma that fractured during or after solidification, allowing hydrothermal fluids to deposit secondary minerals like quartz or calcite into the cracks, subsequently weathered and water-worn into a smooth pebble.
Uses & applications
Used primarily as a decorative beach stone, specimen collecting, or sometimes in landscaping and lapidary work.
Geological facts
Rocks featuring contrasting veins of minerals injected into a host rock are known as veined or brecciated rocks. The smooth, rounded shape indicates extensive transport and polishing by wave action on a beach or riverbed.
Field identification & locations
Easily identified by the striking visual contrast between a dark, fine-grained host rock and lighter hydrothermal veining. Commonly found along beaches, glacial outwashes, and riverbeds where diverse lithologies are deposited.
