ClipArt ETC
This figure, representing Acanthite, an orthrohombic crystal, shows a combination of the following forms: (a), (b), (c), (l), (m), (o), (e), (d), (k), (p), (s), (r), and (n).

Acanthite

This figure, representing Acanthite, an orthrohombic crystal, shows a combination of the following forms:…

This form shows the cube (h), the dodecahedron (d), the tetrahexahedron (f), and the icositetrahedron (l).

Amalgam

This form shows the cube (h), the dodecahedron (d), the tetrahexahedron (f), and the icositetrahedron…

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…

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,…

Iron Sulpharsenide (Arsenopyrite), bounded by ∞P, {110} (M), and 1/3P∞̆, {013} (r), forms penetration twins of two individuals, where P∞̄, {101} acts as twinning plane.

Arsenopyrite

Iron Sulpharsenide (Arsenopyrite), bounded by ∞P, {110} (M), and 1/3P∞̆, {013} (r), forms penetration…

This form shows a crystal of Barium Nitrate exhibiting isometric tetartohedral crystallization.

Barium Nitrate

This form shows a crystal of Barium Nitrate exhibiting isometric tetartohedral crystallization.

This form shows a tetrahedron (o) with its edges beveled by the trigonal tristetrahedron (l), and its angles replaced by the rhombic dodecahedron.

Beveled Tetrahedron

This form shows a tetrahedron (o) with its edges beveled by the trigonal tristetrahedron (l), and its…

This figure represents a crystal of Boron.

Boron

This figure represents a crystal of Boron.

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.

Calcite Crystal; This is one particular habit of a calcite (Calcium Carbonate) crystal.

Calcite

Calcite Crystal; This is one particular habit of a calcite (Calcium Carbonate) crystal.

Calcite Crystal; This is one particular habit of a calcite (Calcium Carbonate) crystal.

Calcite

Calcite Crystal; This is one particular habit of a calcite (Calcium Carbonate) crystal.

This figure shows the combination of forms on calcium hyposulphite (CaS_2_O_3_ + 6 aq). If we assume the face c as the basal pinacoid, and b as the brachypinacoid, then the symbols of the other planes become: (p), (p'), and (q).

Calcium Hyposulphite

This figure shows the combination of forms on calcium hyposulphite (CaS_2_O_3_ + 6 aq). If we assume…

This crystal of Calcium Phosphate, Apatite, represents a complex combination of hexagonal hemihedral forms produced by the pyramidal selection. The nine forms comprise the basal pinacoid ,(P); the prism of the first order, (M); second order, (u); and third order, (h); three pyramids of the first order, (r), (x), and (y); one pyramid of the second order, (s); and one of the third order, (m).

Calcium Phosphate, Apatite

This crystal of Calcium Phosphate, Apatite, represents a complex combination of hexagonal hemihedral…

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 the orthorhombic system, tabular crystals of lead carbonite (cerussite), bounded by the forms ∞P∞̆, {010} (b); ∞P, {110} (m); and P, {111} (p), form groups in which both (m) and ∞P3̆, {130} act as twinning planes.

Cerussite

In the orthorhombic system, tabular crystals of lead carbonite (cerussite), bounded by the forms ∞P∞̆,…

The Copper Sulphide, Chalcocite, forms three kinds of twins symmetrical to ∞P, {110}, to 4/3P∞̆, {043}, and to 1/2P, {112} respectively. The latter is shown in this figure.

Chalcocite

The Copper Sulphide, Chalcocite, forms three kinds of twins symmetrical to ∞P, {110}, to 4/3P∞̆,…

This figure shows an example of Compound Twinning, where two orthoclase twins are twinned in parallel to their basal pinacoid. Compound Twins are produced by the presence of two or more twinning laws in the same group.

Compound Twinning

This figure shows an example of Compound Twinning, where two orthoclase twins are twinned in parallel…

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

Copper Contact Twin

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

This is a crystal of Copper Silicate (Dioptase) with a rhombohedron of the third order, (s), in combination with the prism of the second order, (m), and the negative rhombohedron, (r). This crystal is an example of rhombohedral tetartohedrism in the hexagonal system.

Copper Silicate Showing Rhombohedral Tetartohedrism In the Hexagonal System

This is a crystal of Copper Silicate (Dioptase) with a rhombohedron of the third order, (s), in combination…

A Crystal Aggregate is a union of two or more crystal individuals.

Crystal Aggregate

A Crystal Aggregate is a union of two or more crystal individuals.

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…

A Crystalline Aggregate is mass of crystal grains, devoid of their characteristic forms and closely packed together.

Crystalline Aggregate

A Crystalline Aggregate is mass of crystal grains, devoid of their characteristic forms and closely…

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…

This crystal of Aragonite shows a method of twinning where the twinning plane may change its direction, as when the two symmetrical faces of a prism successively serve as twinning planes.

Cyclic Twinning

This crystal of Aragonite shows a method of twinning where the twinning plane may change its direction,…

This figure shows an example of cyclic twinning on a crystal of Rutile.

Cyclic Twinning on Rutile

This figure shows an example of cyclic twinning on a crystal of Rutile.

Crystal; This form is a combination of an icositetrahedron and a rhombic dodecahedron, where the faces of the icositetrahedron replace the trihedral angles of the dodecahedron. The parameters, m, of the icositetrahedron are less then two.

Dodecahedron

Crystal; This form is a combination of an icositetrahedron and a rhombic dodecahedron, where the faces…

Crystal; This form is a combination of an icositetrahedron and a rhombic dodecahedron, where the faces of the icositetrahedron replace the trihedral angles of the dodecahedron. The parameters, m, of the icositetrahedron are less then two.

Dodecahedron

Crystal; This form is a combination of an icositetrahedron and a rhombic dodecahedron, where the faces…

In cases where the basal pinacoid is fixed by some physical property like cleavage, the elongation is in the direction of the clinodiagonal axis. This crystal of Feldspar shown is a common example of this elongation.

Elongation in the Direction of the Clinodiagonal Axis

In cases where the basal pinacoid is fixed by some physical property like cleavage, the elongation is…

A combination of the cube (h), the octahedron (o), and the dodecahedron (d).

Galena

A combination of the cube (h), the octahedron (o), and the dodecahedron (d).

Gold crystals of the form 3O3, {311}, sometimes resemble combinations of the rhombohedron and scalenohedron.

Gold

Gold crystals of the form 3O3, {311}, sometimes resemble combinations of the rhombohedron and scalenohedron.

"An important part of the study of crystallography consists in the measuring and classifying of the interfacial angles on the crystals of all minerals. These measurements are accomplished by means of instruments known as goniometers." — Ford, 1912

Contact Goniometer

"An important part of the study of crystallography consists in the measuring and classifying of the…

Certain crystals of green fluorspar from Saxony, showing the form ∞ 03, {310}, have one half of their planes developed at the expense of the other half, so as to produce a hexagonal scalenohedron.

Green Fluorspar from Saxony

Certain crystals of green fluorspar from Saxony, showing the form ∞ 03, {310}, have one half of their…

This image represents a twin of the monoclinic mineral Gypsum. Its twinning plane is the orthopinacoid.

Gypsum (Twinning)

This image represents a twin of the monoclinic mineral Gypsum. Its twinning plane is the orthopinacoid.

This image shows a hemihedral crystal of pyroxene, whose forms are (c), (b), (a), (m), (o), and (u).

Hemihedral Crystal of Pyroxene

This image shows a hemihedral crystal of pyroxene, whose forms are (c), (b), (a), (m), (o), and (u).

This figure shows hemimorphism in the direction of the axis of symmetry on a crystal of Pentacid Alcohol (C_6_H_12_O_5_). The forms on this crystal are (c), (p), (r), and (q).

Hemimorphism in the Direction of the Axis of Symmetry

This figure shows hemimorphism in the direction of the axis of symmetry on a crystal of Pentacid Alcohol…

Hemimorphism in the direction of the vertical axis has been observed on crystals of the tetragonal salt, Iodosuccinimide (C_4_H_4_O_2_NI, pictured). Its forms are (p), terminated at one end by (o) and (n), and at the other by (o) only.

Hemimorphism in the Direction of the Vertical Axis

Hemimorphism in the direction of the vertical axis has been observed on crystals of the tetragonal salt,…

This form is bounded by forty-eight similar scalene triangles. Its solid angles are of three kinds: six octahedral, at the extremities of the principal axes; eight hexahedral, at the extremities of the trigonal axes; and twelve tetrahedral, at the extremities of the digonal axes. Naumann's symbol for this form is m 0 n; Dana's, m-n.

Hexoctahedron

This form is bounded by forty-eight similar scalene triangles. Its solid angles are of three kinds:…

This figure reproduces a crystal of Hydrous Copper Sulphate whose forms are (c), (a), (b), (n), (m), (l), and (s).

Hydrous Copper Sulphate

This figure reproduces a crystal of Hydrous Copper Sulphate whose forms are (c), (a), (b), (n), (m),…

This form shows the planes given on a crystal of hydrous nickel sulphate: the basal pinacoid, (c); three pyramids of the second order, (m), (o), and (q); two pyramids of the first order, (n) and (p); and the prisms of the first and second orders, (r) and (s).

Hydrous Nickel Sulphate

This form shows the planes given on a crystal of hydrous nickel sulphate: the basal pinacoid, (c); three…

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 crystal of iron-vitriol has only one plane with an absolutely fixed value, the plane of symmetry, or clinopinacoid (b).

Iron-Vitriol

This crystal of iron-vitriol has only one plane with an absolutely fixed value, the plane of symmetry,…

This image represents an isometric holohedral mirror positioned to produce a cube by reflection.

Isometric Holohedral Mirror

This image represents an isometric holohedral mirror positioned to produce a cube by reflection.

Also known as Stolzite, this crystal is bounded by the unit pyramid of the first order, P, {111} (o), and by the prism of the third order, (p).

Lead Tungstate

Also known as Stolzite, this crystal is bounded by the unit pyramid of the first order, P, {111} (o),…

Crystal; If the alternate planes of the hexoctahedron extend until the intersect, a new for will result. This form, the Pentagonal Icositetrahedron, is bounded by twenty-four similar but unsymmetrical sides. Naumann's symbol for this form is (m0n/2)r, y{lkh}; Miller's is (m0n/2)l, y{klh}; h>k>l. This form is known as 'left-handed' because it contains the left, top plane of the front, upper octant.

Lef-Handed Pentagonal Icositetrahedron

Crystal; If the alternate planes of the hexoctahedron extend until the intersect, a new for will result.…

As shown on this crystal of Magnetite, the octohedron, by the crowding out of two of its opposite faces, may become a rhombohedron.

Magnetite

As shown on this crystal of Magnetite, the octohedron, by the crowding out of two of its opposite faces,…

The most common twinning plane is the orthopinacoid ∞P∞̄ , {100}, as may be seen in this example of malachite.

Malachite

The most common twinning plane is the orthopinacoid ∞P∞̄ , {100}, as may be seen in this example…

This form shows a cube modified by the tetrahedron.

Modified Cube

This form shows a cube modified by the tetrahedron.

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 image represents a twin of the monoclinic mineral Orthoclase. Its twinning plane is the orthopinacoid.

Orthoclase (Twinning)

This image represents a twin of the monoclinic mineral Orthoclase. Its twinning plane is the orthopinacoid.

This is an orthorhombic crystal of olivine. It is formed by the orthorhombic prism in combination with two pinacoids.

Orthorhombic Crystal of Olivine

This is an orthorhombic crystal of olivine. It is formed by the orthorhombic prism in combination with…

This form shows the fundamental prism (p) on a crystal of topaz, in combination with another prism, (p'); the basal pinacoid, (c); the brachydome, (g); and the four pyramids, (o), (o'), (o''), and (x).

Orthorhombic Crystal of Topaz

This form shows the fundamental prism (p) on a crystal of topaz, in combination with another prism,…

This illustration shows a solid state where the orientation is only partial, as in the case of twin crystals. Here, the molecules of each horizontal row have two of their axes parallel with those above and below them, but not the third.

Partial Orientation of Molecules in a Solid

This illustration shows a solid state where the orientation is only partial, as in the case of twin…

A penetration twin of two pentagonal dodecahedrons (known as the iron cross), whose twinning plane is the rhombic dodecahedron, is shown in this figure (Pyrite).

Penetration Twin of Pyrite

A penetration twin of two pentagonal dodecahedrons (known as the iron cross), whose twinning plane is…

This crystal is mainly terminated by a rhombohedron of the third order, (x). With this form are associated the prisms of the first and the second order, (m) and (a); another rhombohedron of the third order, (s), and the two rhombohedrons of the first order, (r).

Phenacite

This crystal is mainly terminated by a rhombohedron of the third order, (x). With this form are associated…

This is a crystal of Polianite, also known as Manganese Dioxide.

Polianite

This is a crystal of Polianite, also known as Manganese Dioxide.

This crystal of Aragonite shows a method of twinning where the twinning plane may remain parallel to itself, so that the alternate individuals are in parallel position. This is called Polysynthetic Twinning.

Polysynthetic Twins

This crystal of Aragonite shows a method of twinning where the twinning plane may remain parallel to…

This form shows a positive and negative tetrahedron in combination.

Positive and Negative Tetrahedron in Combination

This form shows a positive and negative tetrahedron in combination.

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…

"Crystal faces are described according to their relations to the crystallographic axes. A series of numbers which indicate the relative distances by which a face intersects the different axes are called its parameters. " — Ford, 1912

Orthorhombie pyramid

"Crystal faces are described according to their relations to the crystallographic axes. A series of…