Basalt rock is dark colored,fine-grained, and is composed mainly of plagioclase and pyroxene minerals. Granite is light colored,grainy, and is composed mainly of quartz and feldspar. Obsidian rock is a volcanic glass that is chemically unstable. It is usually black but can be other colors (brown,tan, or green). It's composition is similar to granite. Pumice is light colored and extremely porous, and it has a very low specific gravity. Rhyolite is light colored,has a low density and contains 70% silica.
Slate is a very fine grained rock composed of mica flakes. Schist is a medium grade rock with medium to large,flat,sheetlike grains. Gneiss has a distinct banding,it is a medium to coarse grained rock. Marble is a stone with firm structure and slight porosity. It can be various colors do to the variety of minerals present in its content. Quartzite is a hard non-foliated rock that is usually white to gray.
Shale is a fine grained rock composed of clay minerals and quartz. The typical color is gray. Sandstone is gritty to the touch,clastic and is composed of Quartz and or feldspar and can be any color. Coal is usually black and is composed largely of carbon. It is highly combustible. Limestone is chiefly composed of mineral calcite. It is usually in shades of bluish gray to tan. It's texture ranges from coarsely crystalline to very fine grained. Halite is commonly known as rock salt it is typically colorless or white. It is composed of sodium and calcium.