C—white, green, H—5-6 In long, slender 6-sided Amphibole Group brown, black Cl—in two crystals; cleavage angle (Mg,Fe,Ca)₇ directions important in (Si₈O₂₂)(OH)₂ intersecting at differentiating from (may also about 60° and pyroxenes; common in contain Na or 120° metamorphic and some Al) igneous rocks C—gray, dark H—5-6 Crystals short, stout, Pyroxene Group green, black, Cl—in two and 8-sided; cleavage (Mg,Ca,Fe)₂ dark brown, directions angle important in (Si₂O₆) bronze intersecting at differentiating from about 90° amphiboles; common in igneous and some metamorphic rocks C—white, gray, H—6 As crystals, cleavable Feldspar Group pink, light Cl—in two masses and grains; (22) blue, green directions common in igneous and K, Na, Ca, Ba nearly at right metamorphic rocks, also (Al, Si)₄O₈ angles in stream gravel and sand; many varieties C—white when H—7 Finely crystalline Chalcedony pure; may be Cl—none variety of quartz; SiO₂ colored by F—conchoidal botryoidal or impurities concretionary masses; lining in geodes C—colorless, H—7 Most abundant mineral; Quartz (21) white, or F—conchoidal occurs in 6-sided SiO₂ almost any color crystals capped by pyramids, in grains or masses; principal mineral in sandstone, also abundant in igneous and metamorphic rocks; is a variety of silica C—red H—7 A variety of quartz Jasper F—conchoidal usually colored red by SiO₂ hematite inclusions; common in glacial and river sand and gravel found along Lake Michigan shores and in the Mississippi River C—many; H—7 Cloudy banded variety of Agate arranged in F—conchoidal silica; widely used as SiO₂ bands semi-precious stones. Onyx and silicified wood are forms of agate;