Feldspar-Quartz Geode: Hydrothermal fluids from deep within the crust infiltrate and fill fractures in granite. Under suitable conditions (such as a decrease in pressure), small geodes formed by the crystallization of minerals in the hydrothermal fluids are called feldspar-quartz geodes. The flesh-red grains are feldspar crystals, and the translucent grains are quartz crystals.
