"This form consists of twelve scalene triangular faces. These faces correspond in their position to the alternate pairs of faces of a dihexagonal pyramid." — Ford, 1912

Scalenohedron

"This form consists of twelve scalene triangular faces. These faces correspond in their position to…

"...bounded by twelve scalene triangles, and with the general indices {hkl}." -The Encyclopedia Britannica 1910

Scalenohedron

"...bounded by twelve scalene triangles, and with the general indices {hkl}." -The Encyclopedia Britannica…

"The zig-zag lateral edges [of a scalenohedron] coincide with the similar edges of a rhombohedron..." -The Encyclopedia Britannica 1910

Scalenohedron with inscribed Rhombohedron

"The zig-zag lateral edges [of a scalenohedron] coincide with the similar edges of a rhombohedron..."…

"A crystal of scapolite, upon which the faces of the third-order pyramid are shown." — Ford, 1912

Scapolite

"A crystal of scapolite, upon which the faces of the third-order pyramid are shown." — Ford, 1912

This figure shows a combination of forms sometimes observed on the silicate Scapolite, with the unit pyramid, (o); the prisms of the first and second orders, (M) and (b) respectively; and the pyramid of the third order, (s).

Scapolite

This figure shows a combination of forms sometimes observed on the silicate Scapolite, with the unit…

Gold and crystal sceptres from Mycanæ.

Mycanæ:n sceptres

Gold and crystal sceptres from Mycanæ.

"Tetragonal; tri-pyramidal. Crystals usually simple pyramids of first order. Closely resemble isometric octahedrons in angles. Faces of the pyramid of third order are small and rare." — Ford, 1912

Scheelite

"Tetragonal; tri-pyramidal. Crystals usually simple pyramids of first order. Closely resemble isometric…

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which belongs a number of forms having some property in common. In order to classify these different crystals, the existence of certain lines within the crystal, called axes, is assumed, around which the form can be symmetrically build up. These axes are assumed to intersect in the center of the crystal, and to pass through from one side to the other." — Hallock, 1905

Second Right Square Octahedron

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which…

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which belongs a number of forms having some property in common. In order to classify these different crystals, the existence of certain lines within the crystal, called axes, is assumed, around which the form can be symmetrically build up. These axes are assumed to intersect in the center of the crystal, and to pass through from one side to the other." — Hallock, 1905

Second Right Square Prism

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which…

"...to be cut in half by this plane (the twinned plane, reference Twinned Crystal of Gypsum) and one portion to be rotated through 180 degrees about the normal to the same plane. Described as being twinned on the plane." -The Encyclopedia Britannica 1910

Simple Crystal of Gypsum

"...to be cut in half by this plane (the twinned plane, reference Twinned Crystal of Gypsum) and one…

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which belongs a number of forms having some property in common. In order to classify these different crystals, the existence of certain lines within the crystal, called axes, is assumed, around which the form can be symmetrically build up. These axes are assumed to intersect in the center of the crystal, and to pass through from one side to the other." — Hallock, 1905

Six-sided Pyramid

"Science has succeeded in classifying the thousands of known crystals in six systems, to each of which…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is composed of crystals, usually in the form of six-pointed stars.

Snowflakes

A frozen moisture which falls from the atmosphere when the temperature is 32 degrees or lower. It is…

This is a crystal of Sodium Chlorate, exhibiting the tetrahedron (-o) and the pentagonal dodecahedron (p).

Sodium Chlorate

This is a crystal of Sodium Chlorate, exhibiting the tetrahedron (-o) and the pentagonal dodecahedron…

"Isometric; tetrahedral. Tetrahedron form." — Ford, 1912

Sphalerite

"Isometric; tetrahedral. Tetrahedron form." — Ford, 1912

An example of sphenoidal crystallization is Iron-Copper-Sulfide (FeS_2_Cu), also known as chalcopyrite.

Sphenoidal Crystallization

An example of sphenoidal crystallization is Iron-Copper-Sulfide (FeS_2_Cu), also known as chalcopyrite.

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

Spinel Contact Twin

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

Staurolite.

Staurolite

Staurolite.

"Orthohombic. Habit prismatic, showing usually a combination of prism with large angle, brachypinacoid, base and macrodome." — Ford, 1912

Staurolite

"Orthohombic. Habit prismatic, showing usually a combination of prism with large angle, brachypinacoid,…

"...in this figure the thicker lines are the projections of the three planes of symmetry, and on these lie the poles of the rhombehedra (six of which are indicated)." -The Encyclopedia Britannica 1910

Stereographic Projection of a Holosymmetric Rhombohedral Crystal

"...in this figure the thicker lines are the projections of the three planes of symmetry, and on these…

"Monoclinic. Uniform in cruciform twins. Commonly tabular parallel to clinopinacoid. Crystals usually in sheaflike aggregates." — Ford, 1912

Stilbite

"Monoclinic. Uniform in cruciform twins. Commonly tabular parallel to clinopinacoid. Crystals usually…

Sulphur.

Sulphur

Sulphur.

Sulphur.

Sulphur

Sulphur.

"Resinous luster. Color sulphur-yellow, varying with impurities to yellow shades of green, gray, and red. Transparent to opaque. Imperfect conductor of heat." — Ford, 1912

Sulphur

"Resinous luster. Color sulphur-yellow, varying with impurities to yellow shades of green, gray, and…

"Resinous luster. Color sulphur-yellow, varying with impurities to yellow shades of green, gray, and red. Transparent to opaque. Imperfect conductor of heat." — Ford, 1912

Sulphur

"Resinous luster. Color sulphur-yellow, varying with impurities to yellow shades of green, gray, and…

"An allotrope of sulphur, when heated to 115 degrees Celcius, will cool to be yellowish-brown, needle-shaped crystals, derived from an oblique prism." —Hallock 1905

Sulphur

"An allotrope of sulphur, when heated to 115 degrees Celcius, will cool to be yellowish-brown, needle-shaped…

This figure shows an orthorhombic crystal of sulphur, showing the forms: (p), (s), (c), and (n).

Sulphur

This figure shows an orthorhombic crystal of sulphur, showing the forms: (p), (s), (c), and (n).

This figure shows a case of a supplementary twin, formed from two hemimorphic crystals, placed symmetrically to their basal pinacoid (calamine).

Supplementary Twin

This figure shows a case of a supplementary twin, formed from two hemimorphic crystals, placed symmetrically…

"This is bounded by twelve irregular pentagons, and is a tetartohedral or quarter-faced for of the hexakis-octahedron." -The Encyclopedia Britannica 1910

Tetrahedral Pentagonal Dodecahedron

"This is bounded by twelve irregular pentagons, and is a tetartohedral or quarter-faced for of the hexakis-octahedron."…

A tetragonal bipyramidal crystal where the vertical axis is shorter than the horizontal axes.

Tetragonal Bipyramids

A tetragonal bipyramidal crystal where the vertical axis is shorter than the horizontal axes.

A tetragonal bipyramidal crystal where the vertical axis is longer than the horizontal axes.

Tetragonal Bipyramids

A tetragonal bipyramidal crystal where the vertical axis is longer than the horizontal axes.

This figure shows two tetrahedrons with parallel axes, and symmetrically placed with reference to the faces of the cube. The example given is a tetrahedrite crystal.

Tetrahedrite

This figure shows two tetrahedrons with parallel axes, and symmetrically placed with reference to the…

This figure shows a penetration twin of two tetrahedrons, symmetrical to the octohedral face (tetrahedrite).

Tetrahedrite Penetration Twin

This figure shows a penetration twin of two tetrahedrons, symmetrical to the octohedral face (tetrahedrite).

"This is bounded by four equilateral triangles and is identical with the regular tetrahedron of geometry." -The Encyclopedia Britannica 1910

Tetrahedron

"This is bounded by four equilateral triangles and is identical with the regular tetrahedron of geometry."…

This form shows a tetrahedron (o), cube (h), and dodecahedron (d) in combination.

Tetrahedron, Cube, and Dodecahedron in Combination

This form shows a tetrahedron (o), cube (h), and dodecahedron (d) in combination.

"Like the triakis-octahedron, this solid is also bounded b twenty-four isosceles triangles, but here grouped in fours over the cubic faces." -The Encyclopedia Britannica 1910

Tetrakis-hexahedron

"Like the triakis-octahedron, this solid is also bounded b twenty-four isosceles triangles, but here…

"Like the triakis-octahedron, this solid is also bounded b twenty-four isosceles triangles, but here grouped in fours over the cubic faces." -The Encyclopedia Britannica 1910

Tetrakis-hexaheron

"Like the triakis-octahedron, this solid is also bounded b twenty-four isosceles triangles, but here…

"Monoclinic. Crystals varied in habit. Often with prominent basal plane which is steeply inclined and which in combination with short prism and pyramid faces gives a thin wedge-shaped crystal." — Ford, 1912

Titanite

"Monoclinic. Crystals varied in habit. Often with prominent basal plane which is steeply inclined and…

"Monoclinic. Crystals varied in habit. Often with prominent basal plane which is steeply inclined and which in combination with short prism and pyramid faces gives a thin wedge-shaped crystal." — Ford, 1912

Titanite

"Monoclinic. Crystals varied in habit. Often with prominent basal plane which is steeply inclined and…

Topaz.

Topaz

Topaz.

Topaz.

Topaz

Topaz.

Topaz

Topaz

Topaz

"Orthohombic. In prismatic crystals terminated by pyramids, domes, and basal plane." — Ford, 1912

Topaz

"Orthohombic. In prismatic crystals terminated by pyramids, domes, and basal plane." — Ford, 1912

Natural crystal. 4, topaz.

Topaz

Natural crystal. 4, topaz.

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They are also commonly characterized by the presence of three faces of a triangular prism." — Ford, 1912

Tourmaline

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They…

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They are also commonly characterized by the presence of three faces of a triangular prism." — Ford, 1912

Tourmaline

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They…

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They are also commonly characterized by the presence of three faces of a triangular prism." — Ford, 1912

Tourmaline

"Tourmaline crystals show the forms of the Rhombohedral Class but with hemispherical development. They…

"Hexagonal-rhombohedral; hemimorphic. Crystals usually prismatic, vertically striated. A triangular prism, with three faces, prominent, which with the tendency of the prism faces to be vertically striated and to round into each other gives the crystals usually a cross section like a spherical triangle." — Ford, 1912

Tourmaline

"Hexagonal-rhombohedral; hemimorphic. Crystals usually prismatic, vertically striated. A triangular…

"Hexagonal-rhombohedral; hemimorphic. Crystals usually prismatic, vertically striated. A triangular prism, with three faces, prominent, which with the tendency of the prism faces to be vertically striated and to round into each other gives the crystals usually a cross section like a spherical triangle. Crystals are commonly terminated by base and low positive and negative rhombohedrons; sometimes scalenohedrons are present. When the crystals are doubly terminated they usually show different forms at the opposite ends of the vertical axis." — Ford, 1912

Tourmaline

"Hexagonal-rhombohedral; hemimorphic. Crystals usually prismatic, vertically striated. A triangular…

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…