Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a  mineraloid .. The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture (see photo on right). Obsidian is usually an extrusive rock-one that solidifies above Earth's surface. However, it can form in a variety of cooling environments: Black is the most common color of obsidian.
â¢ PEP TALK (noun). The noun PEP TALK has 1 sense: 1. a speech of exhortation attempting to instill enthusiasm and determination in a team or staff. Familiarity information: PEP TALK used as a noun is very rare.
PEP (post-exposure prophylaxis) means taking antiretroviral medicines (ART) after being potentially exposed to HIV to prevent becoming infected. PEP should be used only in emergency situations and must be started within 72 hours after a recent possible exposure to HIV.