"This is the hemihedral form of the hexakis-octahedron and has the indicies {hkl}; it is bounded by twenty-four faces." -The Encyclopedia Britannica 1910

Dyakis-dodecahedron

"This is the hemihedral form of the hexakis-octahedron and has the indicies {hkl}; it is bounded by…

"...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…

"Monoclinic. Crystals are often much elongated parallel to the ortho-axis with a prominent development of the faces of the orthodome zone, giving them a prismatic aspect. Striated parallel to the ortho-axis. Terminated usually at one end of the ortho-axis and most commonly by the two faces of a pyramid." — Ford, 1912

Epidote

"Monoclinic. Crystals are often much elongated parallel to the ortho-axis with a prominent development…

"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

First 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

First Right Square Prism

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

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination." — Ford, 1912

Garnet

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination." — Ford, 1912

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination." — Ford, 1912

Garnet

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination." — Ford, 1912

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination. Hexoctahedron observed at some times." — Ford, 1912

Garnet

"Isometric. Common forms dodecahedron amd trapezohedron, often in combination. Hexoctahedron observed…

"Here the plane of projection is tangent to the sphere, and normals to all the faces are drawn fro mthe centre of the sphere to intersect the plane of projection." -The Encyclopedia Britannica 1910

Gnomonic Projection of a Cubic Crystal

"Here the plane of projection is tangent to the sphere, and normals to all the faces are drawn fro mthe…

"The second form of carbon, known as graphite, is a leaden-gray solid with a metallic luster and a specific gravity of 2 to 2.2, which crystallizes." —Hallock 1905

Graphite

"The second form of carbon, known as graphite, is a leaden-gray solid with a metallic luster and a specific…

Gypsum.

Gypsum

Gypsum.

Gypsum.

Gypsum

Gypsum.

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges beveled by prism and pyramid faces." — Ford, 1912

Gypsum

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges…

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges beveled by prism and pyramid faces. Other forms rare. Sometimes twinned." — Ford, 1912

Gypsum

"Monoclinic. Crystals usually tabular parallel to clinopinacoid; in diamond-shaped crystals with edges…

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing triangular markings." — Ford, 1912

Hematite

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing…

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing triangular markings." — Ford, 1912

Hematite

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing…

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing triangular markings. Edges of plates sometimes beveled with rhombohedral and pyramidal forms." — Ford, 1912

Hematite

"Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often showing…

"...bounded by twelve isosceles trianes each of which are equally inclined to two planes of symmetry." -The Encyclopedia Britannica 1910

Hexagonal Bipyramid

"...bounded by twelve isosceles trianes each of which are equally inclined to two planes of symmetry."…

"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

Hexagonal Prism

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

"Here each face of the octahedron is replaced by six scalene triangles, so that altogether there are fourty-eight faces. This is the greatest number of faces possible for an simple form in crystals." -The Encyclopedia Britannica 1910

Hexakis-octahedron

"Here each face of the octahedron is replaced by six scalene triangles, so that altogether there are…

"The hemihedral form {hkl} of the hexakis-octahedron; it is bounded by twenty-four scalene triangles and is the general form of the class." -The Encyclopedia Britannica 1910

Hexakis-tetrahedron

"The hemihedral form {hkl} of the hexakis-octahedron; it is bounded by twenty-four scalene triangles…

"Bounded by twenty-four trapezoidal faces, and hence somethings called a 'trapezohedron.'" -The Encyclopedia Britannica 1910

Icositetrahedron

"Bounded by twenty-four trapezoidal faces, and hence somethings called a 'trapezohedron.'" -The Encyclopedia…

"Isometric. Trapezohedral habit." — Ford, 1912

Leucite

"Isometric. Trapezohedral habit." — Ford, 1912

This is an illustration of crystals of the inner bark of the locust.

Locust

This is an illustration of crystals of the inner bark of the locust.

"This consists of four faces parallel to the brachy axis." -The Encyclopedia Britannica 1910

Macro-prism and Brachy-pinacoid

"This consists of four faces parallel to the brachy axis." -The Encyclopedia Britannica 1910

"Isometric. Octahedral habit, sometimes twinned octahedrons. Dodecahedron at times, either alone or with octahedron." — Ford, 1912

Magnetite

"Isometric. Octahedral habit, sometimes twinned octahedrons. Dodecahedron at times, either alone or…

"Five kinds of glass are made: flint glass, or crystal; crown glass, broad sheet glass, bottle, or green glass, and plate glass." —The Popular Cyclopedia, 1888

Glass manufacturing

"Five kinds of glass are made: flint glass, or crystal; crown glass, broad sheet glass, bottle, or green…

"Orthorhombic. Crystals commonly tabular parallel to basal plane, showing also short prisms and low brachydomes." — Ford, 1912

Marcasite

"Orthorhombic. Crystals commonly tabular parallel to basal plane, showing also short prisms and low…

"Orthorhombic. Crystals commonly tabular parallel to basal plane, showing also short prisms and low brachydomes. The brachydomes usually striated parallel to the brachy-axis. Often twinned, given coxcomb and spear-shaped groups." — Ford, 1912

Marcasite

"Orthorhombic. Crystals commonly tabular parallel to basal plane, showing also short prisms and low…

"A crystal form does not necessarily make a solid figure. One such an example is this, of the Monoclinic System.

Crystal of the monoclinic system

"A crystal form does not necessarily make a solid figure. One such an example is this, of the Monoclinic…

"The symmetry of the Monoclinic System is as follows: The crystallographic axis b is an axis of binary symmetry and the plane of the a and c axes is a plane of symmetry." — Ford, 1912

Symmetry of monoclinic system

"The symmetry of the Monoclinic System is as follows: The crystallographic axis b is an axis of binary…

An illustration of an octahedral crystal. An octahedron is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex.

Octahedral Crystal

An illustration of an octahedral crystal. An octahedron is a polyhedron with eight faces. A regular…

Represents the combination of an octahedron and a cube, with the octahedron predominate.

Octahedron in Combination with Cube

Represents the combination of an octahedron and a cube, with the octahedron predominate.

Orthoclase

Orthoclase

Orthoclase

Orthoclase.

Orthoclase

Orthoclase.

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base, prism, with often smaller orthodomes." — Ford, 1912

Orthoclase

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base,…

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base, prism, with often smaller orthodomes." — Ford, 1912

Orthoclase

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base,…

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base, prism, with often smaller orthodomes." — Ford, 1912

Orthoclase

"Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base,…

Natural crystals. 5, orthoclase.

Orthoclase

Natural crystals. 5, orthoclase.

"This is the general form and is bounded by eight scalene triangles." -The Encyclopedia Britannica 1910

Orthorhombic Bipyramids

"This is the general form and is bounded by eight scalene triangles." -The Encyclopedia Britannica 1910

"This is the general form and is bounded by eight scalene triangles." -The Encyclopedia Britannica 1910

Orthorhombic Bipyramids

"This is the general form and is bounded by eight scalene triangles." -The Encyclopedia Britannica 1910

"general form...bounded by four scalene triangles." -The Encyclopedia Britannica 1910

Orthorhombic Bisphenoid

"general form...bounded by four scalene triangles." -The Encyclopedia Britannica 1910

"This is bounded by twelve pentagonal faces, but these are not regular pentagons, and the angles over the three sets of different edges are different. The regular dodecahedron of geometry, contained by twelve regular pentagons, is not a possible form in crystals." -The Encyclopedia Britannica 1910

Pentagonal Dodecahedron

"This is bounded by twelve pentagonal faces, but these are not regular pentagons, and the angles over…

"This is the only simple form in this class which differs geometricalled from those of the holosymmetric class...These are each bounded by twenty-four irregular pentagons, and althrough similar to each other they are respectively right- and left-handed..." -The Encyclopedia Britannica 1910

Pentagonal Icositetrahedron

"This is the only simple form in this class which differs geometricalled from those of the holosymmetric…

"At the freezing point [phosphorus] hardens, becomes brittle, and shows, on being broken, evidences of crystalline structure, the crystals being dodecahedral." —Hallock 1905

Phosphorus

"At the freezing point [phosphorus] hardens, becomes brittle, and shows, on being broken, evidences…

"In this the four lateral planes are rectangular and equal; they may be either oblong or square; in the latter case the form is the cube." —The Encyclopedia Britannica, 1903

Primitive Crystal

"In this the four lateral planes are rectangular and equal; they may be either oblong or square; in…

"If the base is a square and the prism stands erect—that is, if its sides or lateral planes, as they are called, are perpendicular to the base—the form is termed a right square prism." —The Encyclopedia Britannica, 1903

Primitive Crystal

"If the base is a square and the prism stands erect—that is, if its sides or lateral planes, as…

"When the base is a rectangle instead of a square, the form is a right rectangular prism." —The Encyclopedia Britannica, 1903

Primitive Crystal

"When the base is a rectangle instead of a square, the form is a right rectangular prism." —The…

"When the base is a rhombus, and the prism stands erect, the form is a right rhombic prism." —The Encyclopedia Britannica, 1903

Primitive Crystal

"When the base is a rhombus, and the prism stands erect, the form is a right rhombic prism." —The…

"When the base is a rhomboid, and the prism stands erect, it is only the opposite laeral faces that can be equal. The form is called a right rhomboidal prism." —The Encyclopedia Britannica, 1903

Primitive Crystal

"When the base is a rhomboid, and the prism stands erect, it is only the opposite laeral faces that…

"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

Orthohombie prism

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

A solid having two parallel polygonal bases connected by triangular faces.

Prismatoid

A solid having two parallel polygonal bases connected by triangular faces.

"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…

Pyroxene

Pyroxene

Pyroxene

Pyroxene

Pyroxene

Pyroxene

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally developed as to give the effect of a hexagonal pyramid." — Ford, 1912

Quartz

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally…

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally developed as to give the effect of a hexagonal pyramid. Sometimes one rhombohedron predominates or occurs alone. At times the prism faces are wanting, and the combination of the two rhombodendrons gives what appears to be a doubly terminated hexagonal pyramid, known as a quartzoid." — Ford, 1912

Quartz

"Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally…

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental crust.

Quartz

This illustration shows Quartz or Silica. Quarts is the most abundant mineral in the Earth's continental…

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to be observed trunctuating the edges between prism and rhombohedron." — Ford, 1912

Left-handed quartz

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to…

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to be observed trunctuating the edges between prism and rhombohedron." — Ford, 1912

Right-handed quartz

"The quartz crystals are said to be right or left handed, depending upon whether these faces are to…