Hardness: The hardness of a mineral idicates how well it resists scratching or abrasion. It is measured on a numerical scale, from 1 (softest) to 10 (hardest). This scale is called Mohs Scale:

Streak: The streak of a mineral is its color when it is ground into a fine powder. This may be done by crushing a mineral fragment, placing the powder on a sheet of white paper, and observing the color. A more common (and convenient) procedure is to rub the mineral firmly across a tile of unglazed white porcelain (called a streak plate) to produce a line of powder whose color is called the streak of a mineral. This property may be distinctive when the color of the mineral is different than that of its streak,since the streak varies only slightly from one specimen to another. Streak is most useful for the identifaction of dark colored minerals such as metallic sulfides and oxides; its usefullnes is more limited when testing light colored sulfates, carbonates or silicates. Also, minerals having a hardness exceeding that of the streak plate (About 6 1/2) cannot be tested in this manner.

Luster: The luster of a mineral is the way its surface reflects light. Luster is governed largely by the surface characteristics of the mineral's atomic structure and is slightly modified by its transparency. Luster should not be confused with color; minerals of different colors may have the same luster. As with color, the luster of a mineral should be observed on a cleavage surface or freshly broken, untarnished surface.

Cleavage: When a mineral has the tendency to break along one or more smooth, flat lustrous surfaces, it is said to have cleavage. The way the mineral breaks is an indication of the way the atoms are arranged within the crystals. Minerals that break easily and cleanly in one or more directions are said to have perfect cleavage. If the break is less clean the cleavage may be described as good, distinct, poor, or none.

Parting: Not to be confused with cleavage is parting, another physical property that is seen when a crystal is broken. Parting surfaces are smooth and flat, and closely resemble cleavage planes, but they are caused by structural imperfections in the mineral and not by the mineral's atomic structure. These imperfections are usually caused by strains that develop within the mineral crystal as it grows, or they may occur as planes of weakness between twin crystals. One crystal may show parting, while another of the same species may not.

Specific Gravity: The relative weight of any substance is referred to as its specific gravity or simply gravity. The specific gravity of a mineral (or any other substance) is given as a number, comparing its weight with an equal volume of water. Thus, a mineral with a specific gravity of 4 is four times as heavy as water.

Fracture: The way a mineral fractures can sometimes help to identify it. Most terms used to describe fracture are listed below.

Tenacity: A mineral's tenacity is its capacity to resist the stress of crushing, tearing, bending, or breaking. Tenacity is usually described by the terms listed below.

Crystal System: Mineral crystals come in a seemingly infinite range of shapes. But behind this tremendous diversity of form there is a strict order, because crystals always grow according to simple mathematical laws. By studying the crystal geometry, crystallographers can fit any crystal into one of only six basic crystal systems. These crystal systems are listed below.

Crystal Habit: Each mineral normally takes one or more characteristic forms, which can be useful in identification. These forms are determined by the manner of crystal growth and aggregation, and may have little or no resemblance to the "ideal" shape of the individual crystal. The term "habit" is used to refer to the minerals preferred mode of growth - that is, to the arrangement and proportion of the faces on the single crystals. Many of the commonly used terms for crystal habit are listed below. There are many others that are fairly self-descriptive.