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This crystal of Tourmaline exhibits hemimorphism in the direction of the vertical axis. Its forms are the prisms, (g), which as a result of hemimorphism, appear as a trigonal prism, and (a); the scalenohedron, (s), and the two rhombohedrons, (R) and (r), at the antilogue pole, while only (R) occurs at the analogue pole.

Tourmaline

This crystal of Tourmaline exhibits hemimorphism in the direction of the vertical axis. Its forms are…

"This solid is bounded by twenty-four isosceles triangles, and may be considered as an octahedron with a low triangular pyramid on each of its faces." -The Encyclopedia Britannica 1910

Triakis-octahedron

"This solid is bounded by twenty-four isosceles triangles, and may be considered as an octahedron with…

"The hemihedral form {hkk} of the icositetrahedron; it is bounded by twelve isosceles triangles arranged in threes over the tetrahedron faces." -The Encyclopedia Britannica 1910

Triakis-tetrahedron

"The hemihedral form {hkk} of the icositetrahedron; it is bounded by twelve isosceles triangles arranged…

"...bounded by six isosceles triangles...indices as in the hexagonal bipyramid." -The Encyclopedia Britannica 1910

Trigonal Bipyramid

"...bounded by six isosceles triangles...indices as in the hexagonal bipyramid." -The Encyclopedia Britannica…

"...bounded by six trapezoidal hedra...derivable from the scalenohedron." -The Encyclopedia Britannica 1910

Trigonal Trapezohedron

"...bounded by six trapezoidal hedra...derivable from the scalenohedron." -The Encyclopedia Britannica…

This figure shows two twin rhombohedrons, symmetrical with reference to a prism of the first order, but without any composition face. There is a complete interpenetration of their substance, and the space common to both is very irregularly distributed between them, as may be shown by an examination in polarized light.

Twin Rhombohedrons

This figure shows two twin rhombohedrons, symmetrical with reference to a prism of the first order,…

"...the two portions are symmetrical with respect to a plane parallel to the ortho-pinacoid." -The Encyclopedia Britannica 1910

Twinned Crystal of Gypsum

"...the two portions are symmetrical with respect to a plane parallel to the ortho-pinacoid." -The Encyclopedia…

This illustration shows the union of a pyramid and a prism of different orders.

Union of a Pyramid and a Prism of Different Orders

This illustration shows the union of a pyramid and a prism of different orders.

This illustration shows the union of a pyramid and a prism of the same order.

Union of a Pyramid and a Prism of the Same Order

This illustration shows the union of a pyramid and a prism of the same order.

This form is a cube with its edges unsymmetrically truncated by the faces of the pentagonal dodecahedron.

Unsymmetrically Truncated Cube

This form is a cube with its edges unsymmetrically truncated by the faces of the pentagonal dodecahedron.

A Urea (CH_4_N_2_O) crystal exhibiting Sphenoidal Crystallization.

Urea

A Urea (CH_4_N_2_O) crystal exhibiting Sphenoidal Crystallization.

The German urn is a 16th century design made out of cut crystal. It is a small vase with a high foot on the bottom.

German Urn

The German urn is a 16th century design made out of cut crystal. It is a small vase with a high foot…

Vesuvianite.

Vesuvianite

Vesuvianite.

Vesuvianite

Vesuvianite

Vesuvianite

"Tetragonal. Prismatic in habit. Often vertically striated. Common forms are prisms of first and second orders, pyramid of first order and base." — Ford, 1912

Vesuvianite

"Tetragonal. Prismatic in habit. Often vertically striated. Common forms are prisms of first and second…

"Tetragonal. Prismatic in habit. Often vertically striated. Common forms are prisms of first and second orders, pyramid of first order and base." — Ford, 1912

Vesuvianite

"Tetragonal. Prismatic in habit. Often vertically striated. Common forms are prisms of first and second…

This form shows a very complex combination of thirteen tetragonal forms occuring on the mineral Vesuvianite: the prism of the first order, (d); prism of the second order, (M); basal pinacoid, (s); three pyramids of the first order, (c), (b), and (u); the ditetragonal prism (f); and the four ditetragonal pyramids (z), (x), (e), and (a).

Vesuvianite

This form shows a very complex combination of thirteen tetragonal forms occuring on the mineral Vesuvianite:…

"Tetragonal; tripyramidal. Crystals usually prismatic. Prominent forms are prisms of the first and second order, pyramid of first." — Ford, 1912

Wernerite

"Tetragonal; tripyramidal. Crystals usually prismatic. Prominent forms are prisms of the first and second…

"Tetragonal; tripyramidal. Crystals usually prismatic. Prominent forms are prisms of the first and second order, pyramid of first. Rarely shows the faces of the pyramid of the third order." — Ford, 1912

Wernerite

"Tetragonal; tripyramidal. Crystals usually prismatic. Prominent forms are prisms of the first and second…

Also known as Fergusonite, this crystal shows the basal pinacoid, (c); the unit pyramid, (s); and the pyramid and prism of the third order, (z) and (r) respectively.

Yttrium Niobate

Also known as Fergusonite, this crystal shows the basal pinacoid, (c); the unit pyramid, (s); and the…

This figure shows a contact twin of Zinc blende, one of the three simplest isometric holohedrons according to the "spinel law".

Zinc blende Contact Twin

This figure shows a contact twin of Zinc blende, one of the three simplest isometric holohedrons according…

Zircon.

Zircon

Zircon.

Zircon.

Zircon

Zircon.

Zircon.

Zircon

Zircon.

Zircon.

Zircon

Zircon.

"Tetragonal. Crystals usually show a simple combination of prism and pyramid of the first order. The prism of the second order and a ditetragonal pyramid also at times observed." — Ford, 1912

Zircon

"Tetragonal. Crystals usually show a simple combination of prism and pyramid of the first order. The…

Natural crystal. 3, zircon.

Zircon

Natural crystal. 3, zircon.