Gabbro

Phaneritic (coarse-grained) texture, Hardness: 6-7 on Mohs scale, Color: dark grey to black with greenish hues, Luster: Vitreous to sub-metallic, Cleavage: discernible in mineral grains, Specific Gravity: 2.7–3.3.

Formed from the slow cooling of magnesium-rich and iron-rich magma inside the Earth's crust (plutonic). It is the intrusive equivalent of basalt and is typically associated with oceanic crust and mid-ocean ridges.

Used as crushed stone for road construction, railroad ballast, and as a decorative stone known as 'black granite' in countertops and cemetery markers.

Gabbro makes up a large part of the Earth's lower oceanic crust. It is often chemically equivalent to basalt, but differs because it cooled slowly underground, allowing large crystals to form.

Identified by its dark color and visible, interlocking crystals of plagioclase feldspar and pyroxene. Commonly found in large plutons or as part of ophiolite complexes. Look for a heavy, dark rock with a 'salt and pepper' look but dominated by the dark 'pepper' (pyroxene).