Читать книгу Earth Materials онлайн

142 страница из 155

ssss1 Common trigonal crystal forms and associated minerals.

Crystal forms Form indices Form description Minerals that commonly exhibit crystal form Rhombohedron Six parallelogram faces inclined to c‐axis Dolomite, calcite, siderite, rhodochrosite, quartz, tourmaline; chabazite Trigonal Scalenohedron 12 scalene triangle faces inclined to c‐axis Calcite Trigonal prism Three rectangular faces parallel to c‐axis Tourmaline, calcite, quartz Trigonal dipyramid Six triangular faces; top three separated from bottom three by a mirror plane Tourmaline

ssss1 Common crystal forms in the orthorhombic crystal system: (a) rhombic dipyramid, (b) front, side, and basal pinacoids, (c) rhombic prism with a pinacoid.

ssss1 Common crystal forms, form indices, and minerals in the orthorhombic system.

Crystal forms Form indices Form description Minerals that commonly exhibit crystal form Rhombic dipyramids {111} {hkl} and variations Eight triangular faces; top four separated from bottom four by a mirror plane Topaz, aragonite, witherite, olivine Rhombic prisms; first, second, and third orders {011} {0kl} {101} {h0l} {011} {0kl} Four rectangular faces parallel to a single crystallographic axis Stibnite, aragonite, barite, celestite, topaz, enstatite, andalusite, cordierite, epidote, olivine Pinacoids; front, side and basal {001} {010} {001} Two parallel faces perpendicular to a‐, b‐ or c‐axis Barite, celestite, olivine, andalusite, topaz, hemimorphite