Minerals are naturally occurring, inorganic substances with characteristic physical and chemical properties. Common examples found in Delaware are quartz (hard, glassy luster), mica (cellophane like pieces), and feldspar (waxy or pearly luster, cleavage). In nature minerals are usually found in mixtures with other minerals. A natural specimen containing several minerals is called "a rock." A common example is granite, which is a mixture of quartz, feldspar, mica, and usually other dark minerals. Fossils are any evidence, direct or indirect, of a pre-existing plant or animal in the rock record. The most popular area for collecting fossils in Delaware is the Chesapeake and Delaware Canal area.