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;
found in glacial gravels
and upper Mesozoic
sediments in southern
Illinois