Apophyllite

Hand Specimen identification: Like prehnite, apophyllite often occurs where zeo-lites occur. Perfect one direction of cleavage, form, color, and luster help identify it.

Chemical Composition : KCa4Si8O20F#8H2O

Hardness : 41 2 to 5

Specific Gravity2.3

Cleavage/Fracture : one perfect (001), poor{110}/uneven

Luster/Transparency : pearly/transparentto translucent

Color : colorless, white, gray

Streak : white

Optical Properties : Apophyllite has negative relief, is colorless, and has very low birefringence. It has perfect (001) cleavage, and often exhibits anomalous interference colors. Uniaxial 1+ 2, v = 1.535, e = 1.537, d = 0.002.

Crystallography : Tetragonal, a = 8.96, c = 15.78, Z = 2; space group P4/m21/n2/c; point group 4/m2/m2/m.

Habit : Apophyllite has a varied habit, including short prisms, pinacoids, and bipyramids. It often has pseudosym-metry, appearing to be combinations of cubes and oc-tahedra.

Structure and composition : Sheets in the apophyllite structure are composed of 4- and 8-member rings of SiO4 tetrahedra. Interlayer Ca, K, and F link the tetrahedral sheets.

Occurrence and associations : Apophyllite is a secondary mineral, which some-times lines openings in basalt and other mafic ig-neous rocks. Associated minerals include zeolites, datolite, calcite, and pectolite.

Varieties :

Related Minerals :

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Prehnite

Hand Specimen identification: Prehnite, although not a zeolite, occurs in many of the same places …

2 comments

  1. I spent a great deal of time to locate something such as this

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