1. plural of biotite; dark-colored mica minerals containing iron and magnesium, commonly found in igneous and metamorphic rocks
Usage: geology; mineralogy

Examples

• The granite sample contained large crystals of biotites that gave it a speckled appearance.
• Geologists identified biotites in the metamorphic rock using their characteristic dark color and perfect cleavage.
• The biotites in the schist were aligned parallel to the foliation planes.
• Under the microscope, the biotites showed strong pleochroism from brown to pale yellow.
• Weathering had altered some of the biotites to chlorite minerals.
• The pegmatite contained unusually large biotites measuring several centimeters across.