Igneous rocks are formed from cooling magma. When this occurs below ground they are referred to as intrusive and the crystals are larger. When the cooling takes place on the surface they are called extrusive igneous rock and the crystals are smaller.
- This collection contains 15 rock specimens grouped by their crystal size and texture
- Each specimen is approximately 1.5 x 1.5" in size and keyed for identification
- The key also includes useful information regarding the rocks composition, structure, texture and formation
- Phaneritic: Pegmatite, Granite, Diabase, Anorthosite, Gabbro
- Porphyritic: Basalt Porphyry, Trachyte
- Aphanitic: Basalt, Rhyolite, Andesite, Tuff, Obsidian, Pitchstone, Pumice, Scoria