Crystal habits of some common minerals

• The crystal habit of a mineral describes its visible external shape. It can apply to an individual crystal or an assembly of crystals

• .

pyrite

Twelve-sided garnet crystals

• Cleavage or fracture: conchodial fracture• Hardness: 7• Color: Red, green, brown• Other diagnostic: equant 12 sided crystals

• Ca, Fe, Mg, Al, Cr, Mn, silicate

Slender tourmaline crystals

Prismatic quartz crystals

• Cleavage or fracture: conchoidal fracture• Hardness: 7• Color: pink, colorless• Diagnostic properties: elongate six sided

crystals

Potassic feldspar

CaAlSi2O8 + NaAlSi2O8

• Cleavage and fracture : two directions at 90o• Hardness: 6• Other diagnositic: Striations (fine lines) on one

of the two cleavage directions ; solid solution between sodium (albite) and calcium (anthornite) plagioclase

• cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.

• There are three main varieties of these crystals:

• Primitive cubic (abbreviated cP[1] and alternatively called simple cubic)

• Body-centered cubic (abbreviated cI[1] or bcc), • Face-centered cubic (abbreviated cF[1] or fcc,

and alternatively called cubic close-packed or ccp)

• Each is subdivided into other variants listed below. Note that although the unit cell in these crystals is conventionally taken to be a cube, the primitive unit cell often is not. This is related to the fact that in most cubic crystal systems, there is more than one atom per cubic unit cell

three crystals of pyrite (FeS2)

• A rock containing three crystals of pyrite (FeS2). The crystal structure of pyrite is primitive cubic, and this is reflected in the cubic symmetry of its natural crystal facets.

reflected in the cubic symmetry of its natural crystal facets.

The three Bravais lattices which form cubic crystal systems are:Pearson symbol: cP

• .

primitive cubic system (cP)

• The primitive cubic system (cP) consists of one lattice point on each corner of the cube. Each atom at a lattice point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom (1⁄8 × 8).

Body-centered cubic

A caesium chloride unit cell

• Each of the two atom types forms a separate primitive cubic lattice, with an atom of one type at the center of each cube of the other type. Altogether, the arrangement of atoms is the same as body-centered cubic

• The body-centered cubic system (cI) has one lattice point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell (1⁄8 × 8 + 1).

function of ionic radius

• more likely to be formed from two elements whose ions are of roughly the same size (for example, ionic radius of Cs+ = 167 pm, and Cl− = 181 pm) .

or "221

• The space group of this structure is called Pm3m (in Hermann–Mauguin notation), or "221

0,0,x > y,0,0 > 0,z,0The ℓ, m, and n directional indices are separated by 90°,

Planes and direction