Answer :
Cubic System
Also known as the isometric system. All three axes are of equal length and intersect at right angles. Based on a square inner structure.
Crystal shapes include:
Cube (diamond, fluorite, pyrite)
Octahedron (diamond, fluorite, magnetite)
Rhombic dodecahedron (garnet, lapis lazuli rarely crystallises)
Icosi-tetrahedron (pyrite, sphalerite)
Hexacisochedron (pyrite).
Common Cubic Crystals:
Diamond Fluorite Garnet
Gold Pyrite Silver
Spinel
Tetragonal System
Two axes are of equal length and are in the same plane, the main axis is either longer or shorter, and all three intersect at right angles.
Based on a rectangular inner structure.
Crystal shapes include:
Four-sided prisms and pyramids
Trapezohedrons
Eight-sided and double pyramids
Icosi-tetrahedron (pyrite, sphalerite)
Hexacisochedron (pyrite).
Common Tetragonal Crystals:
Anatase Apophyllite Chalcopyrite
Rutile Scapolite Scheelite
Wulfenite Zircon
Hexagonal System
Three out of the four axes are in one plane, of the same length, and intersect each other at angles of 60 degrees. The fourth axis is of a different length and intersects the others at right angles.
Based on a hexagonal (6-sided) inner structure.
Crystal shapes include:
Four-sided prisms and pyramids
Twelve-sided pyramids
Double pyramids
Common Hexagonal Crystals:
Apatite Aquamarine Beryl
Cancrinite Emerald Goshenite
Morganite Sugilite Zincite
Trigonal System
(Rhombohedral System) - Axes and angles in this system are similar to the Hexagonal System, and the two systems are often combined as Hexagonal. In the cross-section of a Hexagonal crystal, there will be six sides. In the cross-section of a Trigonal crystal there will be three sides.
Based on a triangular inner structure.
Crystal shapes include:
Three-sided prisms or pyramids
Rhombohedra
Scalenohedra
Common Trigonal Crystals:
Agate Amethyst Aventurine
Calcite Carnelian Citrine
Hematite Jasper Phenakite
Quartz Rhodochrosite Rose Quartz (rarely crystallises)
Ruby Sapphire Smoky Quartz
Tigers Eye Tourmaline
Orthorhombic System
(Rhombic System)Three axes, all of different lengths, are at right angles to each other.
Based on a rhombic (diamond-shaped) inner structure.
Crystal shapes include:
Pinacoids
Rhombic prisms
Pyramids
Double pyramids
Common Orthorhombic Crystals:
Alexandrite Andalusite (Chiastolite) Celestite
Chrysoberyl Chrysoberyl Danburite
Dumortierite Enstatite Hemimorphite
Iolite Tanzanite Topaz
Zoisite
Monoclinic System
There are three axes, each of different lengths. Two are at right angles to each other and the third is inclined.
Based on a parallelogram inner structure.
Crystal shapes include:
Basal pinacoids and prisms with inclined end faces
Common Monoclinic Crystals:
Azurite Chrysocolla Diopside
Epidote Gypsum Hiddenite
Howlite Kunzite Lazulite
Moonstone Muscovite (Mica) Petalite
Serpentine Spodumene Staurolite
Vivianite
Triclinic System
All three axes are of different lengths and inclined towards each other.
Based on a 'triclinic' inner structure, meaning 'three inclined angles'.
Crystal forms are usually paired faces.
Common Triclinic Crystals:
Amazonite Aventurine Feldspar Kyanite
Labradorite Rhodonite Turquoise
Amorphous
No crystal structure. Most of these are either cooled too quickly to crystallise - such as obsidian or moldavite, or are organic - such as amber.
Common Amorphous Minerals:
Amber Moldavite Obsidian
Opal