Metamorphic Rocks

Metamorphism Metamorphic rocks: appear to have changed in their structure or chemical composition since their creation or formation. Originally sedimentary or igneous Altered by heat, pressure, or exposure to hot fluids in earth’s crust

Metamorphism Two kinds: 1. Local metamorphism – rock materials that have been heated and compressed by magma, so their crystal structure and chemical composition has been altered. [Mostly near active volcanoes] 2. Regional metamorphism – large areas of sedimentary rock that were folded in the past due to immense forces. [Mostly during the Flood]

Classifying Metamorphic Rocks 2 kinds: 1. Foliated – contains flattened mineral crystals aligned in parallel layers and may break easily along these layers 2. Nonfoliated – not banded or layered and tend to break into sharp, angular pieces

Foliated Rocks Common foliated rock = slate It is the metamorphosed sedimentary rock shale. In the past, it was used for schoolroom black boards. Colors: black, gray, purple, red, and green

Foliated Rocks Geologists think that schists were formed when slate was deeply buried and exposed to great pressure and temperature. Schist has many thin layers often highly folded and a silky sheen. The same minerals formed dense, foliated, coarsely textured rocks with distinct bands of different minerals called “gneiss” when under greater metamorphic stresses.

Nonfoliated Rocks Common examples: marble and quartzite Marble is metamorphosed limestone. Will fizz when hydrochloric acid is applied “pure” = white (impurities cause color) Uses: monuments, gravestones, and countertops Quartzite is metamorphosed quartz sandstone. Intense heat and pressure made crystals interlock Durable because all pores are filled with silica The Lord is our Rock. (Matt. 7)