GeoTech.org - Minerals

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You own more pieces of quartz than underwear.

Minerals

**Mohs Scale of Hardness**
Scale No.	Mineral Example	Scratch Test	Check out the Mineral Gallery
1	Talc	Easily scratch with fingernail
2	Gypsum	Barely scratch with fingernail
3	Calcite	Barely scratch with copper penny	The resistance that a smooth surface of a mineral offers to scratching is its hardness. Like the other physical properties of minerals, hardness is dependent on the crystal structure. The stronger the binding forces between the atoms, the harder the mineral. The degree of hardness is determined by observing the comparative ease or difficulty with which one mineral is scratched by another, or by file or knife. The hardness of a mineral might then be said to be its "scratchibility". A series of ten common minerals has been chosen as a scale with which the relative hardness of any mineral can be determined. The scale arranged in order of increasing hardness in known as *Mohs Scale of Hardness.*
4	Fluorite	Easily scratch with knife blade
5	Apatite	Barely scratch with knife blade
6	Feldspar	Cannot scratch by blade; easily with glass
7	Quartz	Easily marks steel and glass	Rainbow of Gemstones Gallery
8	Topaz	Harder than common minerals
9	Corundum	Scratches Topaz
10	Diamond	Scratches Corundum; hardest mineral

Cleavage, Parting, and Fracture

Cleavage

A mineral has cleavage if it breaks along definite plane surfaces. Cleavage may be perfect as in the micas, or more or less obscure as in beryl and apatite. In some minerals it is completely absent.

Parting

When minerals break along planes of structural weakness, they have parting. The weakness may result from pressure or twinning; and is parallel to crystalographic directions and thus resembles cleavage. Parting unlike cleavage is not shown in all specimens but only occurs in those that have been twinned or subjected to the proper pressure.

Fracture

The way a mineral breaks when it does not yield alon cleavage or parting surfaces is its fracture. Different kinds of fracture are designated as follows:

choncoidal: The smooth, curved fracture resembling the interior surface of a shell.

fibrous and splintery

hackly: Jagged fractures with sharp edges.

Uneven and irregular: Fractures producing rough and irregular surfaces.

**Tenacity**
Brittle	A mineral that breaks or powders easily.	Tenacity is the resistance that a mineral offers to breaking, crushing, bending, or tearing, is known as tenacity.
Malleable	A mineral that can be hammered out into thin sheets.
Sectile	A mineral that can be cut into thin shavings with a knife.
Ductile	A mineral that can be drawn into wire.
Flexible	A mineral that bends but does not resume it original shape when the pressure is released.
Elastic	A mineral that, after being bent, will resume its original position upon the release of the pressure.

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