See ' porphyritic '. A magnesium-rich member of the mica mineral family. Like all micas, phlogopite forms flat, plate-like crystals that cleave into smooth flakes. A member of the feldspar mineral family. Plagioclase feldspars are silicates that contain considerable sodium and calcium.
Feldspar crystals are stubby prisms, generally white to gray and a glassy luster . .
The theory that the Earth's outer shell is made up of about a dozen lithospheric plates that move about and interact at their boundaries. The earliest Epoch of the Quaternary Period, beginning about 1.6 million years ago and ending 10,000 years ago. Commonly known as the ' Ice Age ', a time with episodes of widespread continental glaciation. . Pliocene The latest Epoch of the Tertiary Period, beginning about 5.3 million years ago and ending 1.6 million years ago. . A large body of intrusive igneous rock that solidified within the crust.