GENERAL GEOLOGY

Detailed explanation-1: -igneous rock, any of various crystalline or glassy rocks formed by the cooling and solidification of molten earth material. Igneous rocks constitute one of the three principal classes of rocks, the others being metamorphic and sedimentary.

Detailed explanation-2: -Igneous rocks are formed from molten rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break.

Detailed explanation-3: -obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite. Obsidian has a glassy lustre and is slightly harder than window glass.

Detailed explanation-4: -…the lustre of nonmetallic minerals: vitreous, having the lustre of a piece of broken glass (this is commonly seen in quartz and many other nonmetallic minerals); resinous, having the lustre of a piece of resin (this is common in sphalerite [ZnS]); pearly, having the lustre of mother-of-pearl (i.e., an iridescent…