Basalt Pebble

Hardness (Mohs): 6. Color: Dark grey to black. Luster: Dull/Earthy. Structure: Aphanitic (fine-grained), sometimes vesicular. Cleavage: None. Specific Gravity: 2.8 - 3.0.

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet. The rounded shape suggests fluvial erosion or coastal wave action. Given the coordinates in Taiwan, this is likely part of the volcanic arc terrain or transported by rivers from same.

Used in heavy construction, road base, crushed stone, and as a material for 'hot stone' therapy. Handheld pebbles are often used as simple decorative garden stones.

Basalt is the most common volcanic rock on Earth and makes up most of the ocean floor. The Moon's dark plains, the lunar maria, are also composed of basalt.

Identify by its dark matte color, weight (denser than most light-colored rocks), and fine grain where individual crystals are not visible to the naked eye. Extremely common in the volcanic regions of Taiwan and along its eastern coastline.