Minerals

thick sheets stacked together

elongate crystals that are flattened in one direction

composed of hair-like crystals

no clear shapes visible

the shape of broken surfaces on a mineral crystal which is controlled by the strength of chemical bonds in various directions

• form of smooth, planar (flattened) breakage parallel to planes (flat surfaces) • generally described by the number of clear directions and the angle between them

one well-developed planar (flat surface) cleavage

two cleavages

three cleavages at right angles

three cleavages not at right angles

four cleavages

non-planar, irregular form of breakage

rough surface

curved surfaces like broken glass

jagged and sharp

long fibers

mineral’s resistance from scraping

softer than a finger nail (H<2.5)

harder than a fingernail softer than a penny (2.5>H>3)

harder than penny, softer than knife blade (3>H>5.5)

harder than knife blade, softer than porcelain (5.5<H<6.5)

Harder than porcelain streak plate (H>6.5)