The 6 Characteristics
The characteristics of minerals can be a clue to their identity but cannot decide it.
The characteristics are...
-colour
-lustre
-cleavage and fracture
-crystal structure
-hardness
-streak
The characteristics are...
-colour
-lustre
-cleavage and fracture
-crystal structure
-hardness
-streak
Colour
Color is not always a good clue to the identity of a mineral. Many minerals are sometimes different colors and many minerals have extra chemicals in them that give them an unexpected color. Also, weathering may change the color of the mineral. Usually, we notice the color of a mineral first but Some minerals are easily identified by color because they are never change color. For example, malachite is always green. Keep in mind, however, that color by itself isn't enough to identify a mineral. Chemical impurities can change the color of a mineral without changing its basic make-up. For example, quartz in its purest form is colorless and clear as glass. Quartz with traces of iron becomes violet/amethyst. With traces of manganese, it turns pink /rose quartz. If quartz is exposed to radiation, it turns brown or smoky/quartz.
Cleavage and Fracture
Cleavage is breakage of a mineral along planes of weakness on the structure of the mineral. Fracture is breakage not along planes of weakness on minerals, for example galena breaks into little cubes, mica breaks into thin sheets, also Calcite breaks into slanting brick-like pieces, feldspar breaks into little step-like pieces, and quartz breaks into mixed up different pieces.
Crystal Structure
Crystal Structure is a geometric shape of a crystal or mineral. Minerals grow in specific shapes and usually crystallize into one of the six systems. Crystals are usually shaped like blocks with similar or symmetrical faces. The crystal has 3 axes to symmetrical all at right angles and the same length to each other.
Lustre
Lustre is a description of the way light interacts with the surface of a mineral. It has nothing to do with the colour or shape of the mineral but is related to transparency, surface conditions, crystal habit and index of refraction. The terms in the list below are general not scientific but are meant as descriptive language. The list below includes the most commonly used terms.
-Adamantine, very gem-like crystals
-Dull, a non reflective surface of any kind
-Earthy, the look of dirt or dried mud
-Fibrous, the look of fibers
-Greasy, the look of grease
-Gumdrop, the look of sucked on hard candy
-Metallic, the look of metals
-Pearly, the look of pearls
-Pitchy, the look of tar
-Resinous, the look of resins such as dried glue or chewing gum
-Silky, the look of silk similar but more compact then Fibrous
-Sub-metallic, a poor metallic lustre
-Vitreous, the most common lustre that simply means the look of glass
-Waxy, the look of wax
-Adamantine, very gem-like crystals
-Dull, a non reflective surface of any kind
-Earthy, the look of dirt or dried mud
-Fibrous, the look of fibers
-Greasy, the look of grease
-Gumdrop, the look of sucked on hard candy
-Metallic, the look of metals
-Pearly, the look of pearls
-Pitchy, the look of tar
-Resinous, the look of resins such as dried glue or chewing gum
-Silky, the look of silk similar but more compact then Fibrous
-Sub-metallic, a poor metallic lustre
-Vitreous, the most common lustre that simply means the look of glass
-Waxy, the look of wax
Hardness
All properties are good properties to identifying minerals but in terms of reliability hardness is a better ones. One of the oldest ways of measuring hardness is the Mohs Hardness Scale, created by the german mineralologist Friedrich Mohs in 1812. Hardness measurements are widely used. Hardness is a measure of a minerals resistance to being scratched, How can hardness be used to identify minerals? That is what German scientist Friedrich Mohs asked himself in 1812. He developed a scale of ten minerals and their hardness.
Streak
The streak of a mineral is the colour of the powder produced when it is scratched. When a mineral is rubbed against a piece of unglazed porcelain title it leaves a streak. The hardness value of porcelain tile is seven so minerals with a hardness greater then seven do not leave a streak on the title. Pencil marks are graphite streaks that are soft enough to be left on a piece of paper. A streak test is one way to identify whether a mineral sample is gold or pyrite.