Oyster / muscle shells
Teeth
Crystal
o
Single, continuous, piece of crystalline solid
o
Bound by flat surfaces (crystal faces) with regular geometric form occurring naturally
o
Consistency of interfacial angles
o
The same mineral has the same crystal faces and angles between them
o
Crystal examples:
o
Diamond, quartz, garnet, etc.
o
Crystals interact with light to create attractive beauty
o
X-Ray Diffraction (XRD) proposed by
Max van Laue
is still used to look inside crystals
o
The order of the atoms in a crystal repeat regularly in three dimensions
o
This is called
Crystal Lattice
o
The order of these atoms display symmetry, and this order defines the crystal structure
o
Physical properties of crystal depend on:
o
Identity of atoms
o
Arrangement of atoms
o
Nature of atomic bonds
o
Diamond
and graphite
are made entirely of Carbon
o
Diamond
- atoms are arranged in tetrahedral (hardest mineral)
o
Graphite
– atoms arranged in sheets; softest mineral
o
Polymorph
– same composition, different structure
Mineral Formation
o
New crystals form in 5 different ways:
o
Solidification from a melt
o
Crystals grow when the melt cools
o
Liquid freezes to form solid
o
Precipitation from solution
o
Seeds form when precipitation becomes saturated
o
Solid State diffusion
o
Garnets
o
Biomineralization
o
Our tooth enamel is mineral apatite
o
Precipitating from Gas
o
Tiny early crystal acts as seed for growth
o
Atoms migrate to seed and attach
o
Growth moves face outward from center
o
Sometimes if crystals grow in confined spaces, they don’t have faces, as the faces are obstructed by objects
around the crystal
o
Anhedral
– grown in tight space, no faces
o
Euhedral
– grown in open cavity, good faces
Mineral Destruction
o
Minerals can be destroyed by:
o
Melting – heat breaks the bonds holding atoms together
o
Dissolving – solvents break atomic bonds
o
Chemical reaction – reactive materials break bonds
Mineral Physical Properties:
o
Color
o
Streak
o
Color of powder produced from crushing a mineral
o
Luster
o
The way mineral surface scatters light, metallic, or non-metallic
o
Hardness
o
Scratching resistance
o
Derives from strength of atomic bonds
o
Specific gravity
o
Density of mineral
o
How heavy it feels
o
Crystal habit
o
Shape characteristics
o
Is it a single crystal with well-formed faces, an aggregate of many well-formed crystals
o
Records variation in directional growth
Block = same speed growth in all directions
Needle-like = fast growth in only one direction
o
Fracture or cleavage
o
Minerals break in ways that reflect their atomic bonds
o
Fracturing implies equal bond strength in all directions
o
Cleavage – tendancy to break along planes of weaker atomic bonds
Produces flat, shiny surfaces
Cleavage is all through the crystal, usually produces parallel steps, where crystal faces only occur
on external faces
Mineral Classification
o
Minerals can be broken into a few groups.
J. J. Berzelius, a Swedish chemist, noted similarities
o
Minerals can be separated by:
o
