Mariposite is a word that has been used in many ways. It can refer to green mica minerals, or metamorphic rocks that contain enough green mica to impart a green color. Gold prospectors learned that gold could be found in areas where these green rocks were present. This is because mariposite is an ore of gold.

Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. It is composed primarily of calcium carbonate. The specimen shown above is about two inches (five centimeters) across.

Mariposite is a word that has been used in many ways. It can refer to green mica minerals, or metamorphic rocks that contain enough green mica to impart a green color. Gold prospectors learned that gold could be found in areas where these green rocks were present. This is because mariposite is an ore of gold.

Hornfels is a fine-grained nonfoliated metamorphic rock with no specific composition. It is produced by contact metamorphism. Hornfels is a rock that was “baked” while near a heat source such as a magma chamber, sill, or dike. The specimen shown above is about two inches (five centimeters) across.

Lapis Lazuli, the famous blue gem material, is actually a metamorphic rock. Most people are surprised to learn that, so we added it to this photo collection as a surprise. Blue rocks are rare, and we bet that it captured your eye. The round objects in the photo are lapis lazuli beads about 9/16 inch…

Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals. The specimen shown above is about two inches (five centimeters) across.

Anthracite is the highest rank of coal. It has been exposed to enough heat and pressure that most of the oxygen and hydrogen have been driven off, leaving a high-carbon material behind. It has a bright, lustrous appearance and breaks with a semi-conchoidal fracture. It is often referred to as “hard coal”; however, this is a…

Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth’s surface. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks. There are two basic types of metamorphic rocks. Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat…