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This figure reproduces a combination of orthorhombic forms observed on crystals of aluminum orthosilicate, or Andalusite: (a), (b), (c), (m), (l), (n), (r), (p), (s), and (k).

Andalusite

This figure reproduces a combination of orthorhombic forms observed on crystals of aluminum orthosilicate,…

This figure shows a crystal of basic Zinc Silicate (calamine, hemimorphite) showing hemimorphism.

Calamine, Hemimorphite

This figure shows a crystal of basic Zinc Silicate (calamine, hemimorphite) showing hemimorphism.

Also known as Diopside, this crystal exhibits symbols whose forms are: (c), (b), (a), (m), (o), and (u).

Calcium-Magnesium Metasilicate

Also known as Diopside, this crystal exhibits symbols whose forms are: (c), (b), (a), (m), (o), and…

In some cases, the elongation of a crystal may be in the direction of the orthogonal axis, whose position is determined by the plane of symmetry. This crystal of the silicate mineral, Epidote, shows an example of this.

Elongation in the Direction of the Orthogonal Axis

In some cases, the elongation of a crystal may be in the direction of the orthogonal axis, whose position…

This figure exhibits a combination occurring on the ferro-magnesian meta-silicate, Hypersthene. Forms: (a), (b), (m), (n), (h), (o), (c), (i), and (u).

Hypersthene

This figure exhibits a combination occurring on the ferro-magnesian meta-silicate, Hypersthene. Forms:…

This figure shows a crystal of Orthoclase, exhibiting forms (M), (P), (T), (x), (y), (o), and (n).

Orthoclase

This figure shows a crystal of Orthoclase, exhibiting forms (M), (P), (T), (x), (y), (o), and (n).

This figure shows a crystal of Rhodonite (manganese meta-silicate), whose forms are: (c), (b), (a), (n), (h), (o), and (s).

Rhodonite

This figure shows a crystal of Rhodonite (manganese meta-silicate), whose forms are: (c), (b), (a),…

An alternate combination of manganese meta-silicate (Rhodonite), showing forms: (c), (b), (a), (n), (h), (o), and (s).

Rhodonite

An alternate combination of manganese meta-silicate (Rhodonite), showing forms: (c), (b), (a), (n),…

Striation of crystal planes may be produced by repeated polysynthetic twinning. This is well illustrated in the case of the triclinic feldspar, Albite. The twinning plane here is the brachypinacoid, and the contact of a large number of fine lamellæ, alternately in twinning position, would evidently produce a striation on the basal plane parallel to the brachydiagonal axis

Striation of Crystal Planes

Striation of crystal planes may be produced by repeated polysynthetic twinning. This is well illustrated…