What is a variable speed drive? A variable speed drive is a piece of equipment that regulates the speed and rotational force, or torque output, of an electric motor. The background and technology. There are millions of motors in use in industry and offices around the world.
The specific gravity for Obsidian is 2.35, it's refractive index is 1.48-1.51, and it's double refraction is None. History Obsidian is named after a Roman, Obsius.
Scoria is the vesicular ejecta of mafic to intermediate magmas such as basalt and andesite. Scoria is generally a dark brownish black or red. Its specific gravity ranges from 0.8 to 2.1. Scoria is generally thought of as the mafic version of pumice. It forms when magma rich in dissolved gases is vented. As the magma encounters lower pressures, the gases are able to escape and form vessicles.