        
|
ColorAlthough color is the most obvious, it is the least reliable. Notice the picture above, these are all specimens of the mineral- calcite. Some minerals are always the same color, however, such as Sulfur, and Pyrite.Streak
When an unknown mineral is rubbed against a piece of unglazed porcelain ( aka-streak plate) it may produce a colored line. This color will help to determine the minerals identification. This test is very useful for Hematite and Limonite. Many times a sample does not leave a color streak however, or is harder than the streak plate. The above are the minerals Galena and Hematite. Both have metallic lusters and seem heavy for their relative sizes. Hematite has a red brown streak. Have you figured which one is Hematite.Fracture and Cleavage
These terms describe the way a mineral breaks. If a mineral fractures, it breaks along rough edges. If it cleaves, then it breaks along smooth, flat surfaces. Notice the illustration, this Biotite cleaves into flat sheets on the top, but it fractures on the sides. Some rocks also have a type of cleavage called slaty cleavage. This is not the same type of cleavage exhibited by a mineral. Cleavage found in minerals is the the result of the way the chemicals bond together, but in rocks, it is the result of the way the minerals align themselves parallel to one another.
When some minerals fracture, they appear to break along long curved surfaces (that look like a shell) like that shown above. This type of fracture is known as conchoidal fracture and Quartz and the igneous rock Obsidian will demonstrate this type of fracture. The rough, irregular breaking is known as hackly fracture. Hardness
This is how resistant a mineral is to being scratched. We use the Mohs scale to classify a given minerals hardness. If we have a sample that we can scratch with Fluorite, but not with Gypsum, we can predict that the samples hardness is around 3. But if you forgot your hardness scale minerals at home (and don't we all sometimes) we can use a simple field method. The technique used is rather similar. All you do is try to scratch the unknown mineral with various items, such as a fingernail (hardness of about 2.5), a penny (3), a steel nail (5.5) and a steel file (7). The item that first scratches the unknown is harder than the unknown so now you must estimate. Below is the Mohs Scale.
Luster
The way a mineral reflects light. Does your mineral appear to be a metal (metallic luster)? Or does it look like a nonmetal (nonmetallic luster)? There are several other words used to describe luster, but in the idea of keeping it simple I will use only these. If you use the flowchart provided below, you will better understand my reasons. Notice the sample above. The way light reflects off the mineral give a clue to its identity. Can you tell that this is a metal? (native Copper)Crystal form
The mineral above is easily identified as quartz primarily by its six-sided crystal form (hexagonal). The way the outside of this mineral looks is an expression of the arrangement of its atoms. This external expression is known as a crystal. Its crystal structure is the result of regular grouping of atoms that are homogeneous (having the same characteristics throughout the crystal).A crystal is a polyhedral form, which means it is a geometric solid. It has a specific set of faces, corners and edges, which is consistent with the geometric packing of the atoms.There are 6 basic crystal forms. The form that the unknown demonstrates is a good clue to its identity.TasteThis will quickly identify the mineral halite (salt). If you are new to this process you must use this one with caution, as you never know what the unknown may be. Often, you may need to resort to this method (until you more fully understand other identifying traits) to differentiate halite from calcite. If you do taste the sample (especially in a class environment) you should realize that it has been handled by and probably tasted by hundreds of others.Specific GravityThis characteristic relates to the minerals density. If the mineral is heavy for its size, then it has a high specific gravity. Water displacement is useful in determining specific gravity. Thank you Archimedes!MagnetismIs this mineral magnetic (try using a compass), or is it attracted by a magnet? This property is characteristic of Magnetite.
|
