Thin section micrograph, in transient cross-polarized light, of crystalline quartz with inclusions. Quartz is a very widespread mineral formed of silica and oxygen (silicon dioxide, SiO2) and occurring in many varieties and environments. Most quartz on earth occurs as sand grains and as an inconspicuous rock component. Well-developed and clear crystalline quartz forms in open fractures or voids inside rocks. During or after crystallization gas bubbles or extraneous minerals may form or become trapped in the growing crystal, appearing in different forms, such as blobs, spots, specks, phantoms, needles, etc. |