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The form 3O3, {311} on Ammonium Chloride (Sal Ammoniac) may have only six of its twenty-four planes developed, and in this way give rise to a form resembling a tetragonal trapezohedron.

Ammonium Chloride

The form 3O3, {311} on Ammonium Chloride (Sal Ammoniac) may have only six of its twenty-four planes…

Natural crystals. 2, beryl.

Beryl

Natural crystals. 2, beryl.

A tetrahedron crystal of Boracite

Boracite Crystal

A tetrahedron crystal of Boracite

A cube crystal of Boracite

Boracite Crystal

A cube crystal of Boracite

A rhombic dodecahedron crystal of Boracite

Boracite Crystal

A rhombic dodecahedron crystal of Boracite

This figure represents a crystal of Boron.

Boron

This figure represents a crystal of Boron.

Rhombohedron calcite crystal

Calcite

Rhombohedron calcite crystal

A flat rhombohedron calcite crystal

Calcite

A flat rhombohedron calcite crystal

An acute rhombohedron calcite crystal

Calcite

An acute rhombohedron calcite crystal

A prism and rhombohedron calcite crystal

Calcite

A prism and rhombohedron calcite crystal

A scalenohedron and rhombohedron calcite crystal

Calcite

A scalenohedron and rhombohedron calcite crystal

A basal pinacoid, prism, and rhoombohedron calcite crystal

Calcite

A basal pinacoid, prism, and rhoombohedron calcite crystal

A calcite crystal

Calcite

A calcite crystal

A calcite crystal

Calcite

A calcite crystal

A calcite crystal

Calcite

A calcite crystal

A calcite crystal

Calcite

A calcite crystal

This figure represents a crystal of iron pyrite showing representatives of all the forms of the isometric system except the rhombic dodecahedron: ∞O∞ {100} (P); O, {111} (d); [∞O2/2], π{102} (e); [4O2/2], π{214} (s); 2O2, {211} (o); and 3O, {133} (t). It is shortened in the direction of one of the principal axes, which, together with the fact that only two of the three faces belonging to the forms s, o, and t are developed in each octant, gives to it a decidedly orthorhombic habit.

Crystal of Iron Pyrite Showing Representatives of All the Forms of the Isometric System

This figure represents a crystal of iron pyrite showing representatives of all the forms of the isometric…

Forms of crystals.

Crystals, Forms of

Forms of crystals.

Cubes of Iron Pyrites frequently show a striation of their planes in one direction, which is perpendicular to the striation on all contiguous faces, owing to oscillatory combination with the pentagonal dodecahedron. This would not be possible in a holohedral cube.

Cube of Iron Pyrite

Cubes of Iron Pyrites frequently show a striation of their planes in one direction, which is perpendicular…

Curvature of crystal planes is quite a constant property of some substances. It may be due to a very fine oscillatory combinations or to an irregularity of growth and a want of perfect parallelism between sub-individuals. A common instance is the Diamond, whose faces, except those of the octahedron, are almost always curved.

Curvature of Crystal Planes (Diamond)

Curvature of crystal planes is quite a constant property of some substances. It may be due to a very…

"...shows two crystals of tartaric acid, a a right-handed crystal of dextro-tartaric acid, and b a left-handed crystal of laevo-tartaric acid. The two crystals are enantimorphous." -The Encyclopedia Britannica 1910

Enantimorphous Crystals of Tartaric Acid

"...shows two crystals of tartaric acid, a a right-handed crystal of dextro-tartaric acid, and b a left-handed…

"A concretionary stone or pebble, hollow inside, and often having the walls of the cavity lined with crystals." -Whitney, 1911

Quartz Geode

"A concretionary stone or pebble, hollow inside, and often having the walls of the cavity lined with…

"Goniometer. An instrument for measuring solid angles, or the inclination of planes, particularly the angles formed by the faces of crystals." -Whitney, 1911

Hand Goniometer

"Goniometer. An instrument for measuring solid angles, or the inclination of planes, particularly the…

"Goniometer. An instrument for measuring solid angles, or the inclination of planes, particularly the angles formed by the faces of crystals." -Whitney, 1911

Reflection Goniometer

"Goniometer. An instrument for measuring solid angles, or the inclination of planes, particularly the…

The icositetrahedron, 4O4, {411}, on potassium chloride sometimes produces an apparent rhombohedron by the survival of only one fourth of its planes. Two such rhombohedrons, in apparent twinning position, may be derived from the planes of the same icositetrahedron.

Potassium Chloride

The icositetrahedron, 4O4, {411}, on potassium chloride sometimes produces an apparent rhombohedron…

It has been observed that the pentagonal dodecahedron, [∞o2/2], π {201}, on pyrite may have but six of its twelve planes developed in such a manner a to produce an apparent rhombohedron.

Pyrite

It has been observed that the pentagonal dodecahedron, [∞o2/2], π {201}, on pyrite may have but six…

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…

"Zircon, a mineral composed of of zirconium silicate, sometimes used as a gem-stone... THe mineral crystallizes in the tetragonal system, generally in combinations of square prisms and square pyramids" (Britannica, 1910).

Zircon

"Zircon, a mineral composed of of zirconium silicate, sometimes used as a gem-stone... THe mineral crystallizes…

"Zircon, a mineral composed of of zirconium silicate, sometimes used as a gem-stone... THe mineral crystallizes in the tetragonal system, generally in combinations of square prisms and square pyramids." -Britannica, 1910

Zircon

"Zircon, a mineral composed of of zirconium silicate, sometimes used as a gem-stone... THe mineral crystallizes…