Identification of Minerals

1. Identification of Minerals

2. How can a Mineral be Identified • Each mineral has a definite chemical composition and crystalline structure. • These two characteristics are the fingerprint of the mineral • Various chemical tests in laboratories can be done on a mineral to determine its composition. • X-ray diffraction can be used to determine its crystalline structure.

3. The procedures in the laboratories are time consuming and costly. • Of the 4000 minerals, only 20 are common, so identification becomes easier, as they can be determined for the most part by their physical characteristics. • The process still take practice and good observation skills

4. Physical Properties for Identification of Minerals • Colour • Streak • Crystal habit • Hardness • Cleavage • Fracture • Lustre • Specific gravity

5. Colour • The most obvious, but least reliable. • Many minerals can be found in different colours. • Example is Quartz – white, clear, purple, brown, pink, and black

6. Streak • This test is very reliable. • Streak is the colour of the mineral in powder form. • The colour is found by scratching the mineral against a piece of porcelain (called a streak plate).

7. External Crystal Habit • The shape that we see of the mineral maybe a clue. • Some common crystal habits are:

8. A crystal is an external expression of a mineral’s internal arrangement of atoms. All minerals have an orderly internal arrangement of atoms, but crystals are rarely observed in nature. • Minerals do not always form there natural characteristic because they are competing for space when they are growing. Therefore they need room to grow. • This means the mineral must either have the strength to grow in a space, or have an environment that allows for growth.

9. Hardness • This is the minerals resistance to scratching. • The degree of hardness is indicated with a number on the Moh’s Hardness Scale

10. Cleavage • Cleavage is the tendency of some minerals, when struck to break along distinct planes. • These planes represent areas of weak bonding in the mineral’s crystal structure. • A mineral may cleave; • In one plane • Two planes at 90º • Two planes at angles other than 90º • Three planes at 90º • Three planes at angles other than 90º • Or a mineral may not cleave, which is called fracture

12. Lustre • The lustreof a mineral is the way its surface reflects light. • Most terms used to describe lustre are self-explanatory: metallic, earthy, waxy, greasy, vitreous (glassy), adamantine (or brilliant, as in a faceted diamond). • It will be necessary, at least at first, only to distinguish between minerals with a metallic lustre and those with one of the non-metallic lustres. • A metallic lustre is a shiny, opaque appearance similar to a bright chrome bumper on an automobile. • Other shiny, but somewhat translucent or transparent lustres (glassy, adamantine), along with dull, earthy, waxy, and resinous lustres, are grouped as non-metallic.

14. Specific Gravity • The specific gravity of a substance is a comparison of its density to that of water. • Specific gravity can be measured precisely, or estimated by a comparison. • To compare the specific gravity of any two minerals, simply hold a sample of one in your hand and "heft it," i.e., get a feeling for its weight. • Then heft a sample of the other that is approximately the same size. • If there is a great difference in specific gravity, you will detect it easily. It is often sufficient to note whether a mineral's specific gravity is significantly higher or lower than that of other minerals.

15. These physical characteristics should be used in combination to identify a mineral. • A Mineral Identification Key is a good tool to use when start out with the identification of minerals