Likely basalt

Dark gray to black, fine-grained and massive, with a dull to subtly vitreous luster; Mohs hardness about 5–6, typically dense (specific gravity ~2.8–3.0), with no obvious cleavage in the specimen.

An extrusive igneous rock formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface. Most examples are geologically young compared with continental rocks, ranging from recent lava flows to Precambrian volcanic formations.

Used extensively as crushed aggregate, road base, railway ballast, riprap, and dimension stone; attractive polished pieces are used decoratively. Common specimens usually have modest collector value.

Basalt is the most widespread volcanic rock and forms much of the oceanic crust, including seafloor and many large shield volcanoes. Vesicles, if present, may later fill with zeolites, quartz, or calcite.

Identify it by its uniformly dark color, heavy feel, fine texture, and lack of visible large crystals; a streak test is usually gray, and a magnet may show weak attraction if magnetite is present. Common in volcanic regions, oceanic islands, mid-ocean ridges, and flood-basalt provinces.