Specific Gravity

The familiar physical property is able to get rid of a lot of possibilities and is in many cases done right after the hardness test has been done. This test is done by weighing the weight of a mineral specimen with the weight of the same volume of water (scientifically). Since minerals have a lot different shapes to them, determining the exact volume of a specimen is almost impossible to accomplish.

Nonetheless, the specimen can be weighed in air on a spring scale and dunked into water obtaining another weight reading. The specific gravity is set by diving the weight in the air by the loss of the weight in the water. Just to give you an example of this, let’s say you have a specimen that weighs twenty ounces in the air and sixteen ounces in the water, this would mean that the specific gravity would be of five.

Keep in mind though that this test is only a rough calculation as the precision of the scale as well as the pureness of the water can influence the ending result. If this test is to be done in the field you will need to make sure that the water you use comes from a fresh water source and not from a saline lake because salt can bring down the weight in the water.

Some other methods of identifying minerals are by cleavage and fracture. Unless they are minerals, almost all minerals will break if they are hit hardly. If they break irregularly, it is said they fracture. If the mineral breaks along regular lines or patterns it shows cleavage.

While it is true that there are different ways of identifying minerals and some of them are very effective, some of them are not worth it due to the fact that many minerals fall into the same classification.

Cleavage: when a mineral is struck at very sharply with a hammer for example it might cause the mineral to shatter into little pieces. Check the pieces to see if they have lines that correspond to minerals original crystal structure, as this will indicate a lot about the mineral. For example, galena crystals have three axes of the same length and at right angles. When this mineral is shattered it breaks up into little cubes. 

Mineral Fracture
Fracture: there are a lot of minerals that shatter in different ways when they are hit with a hammer even in cases where they do not show cleavage. When this takes place it is said to break and the broken surfaces can in many occasions help you identify them.

There are different types of fractures however there are only some that the prospector will be interested in. some of the most important ones have been listed as well as a mineral in order to exemplify them:

Conchoidal fracture: Explains the way that brittle materials break when they do not follow any natural planes of separation. It breaks like the smooth surface of a sea shell and is alike the pieces that can be found in thick pieces of broken glass. Can be found in obsidian and most quartz.

Splintery or fibrous fracture: These are splinters or fibers that can be found on the surface such as what occurs to pectolite.

Hackly fracture: This is a surface that is rough and has jagged torn edges such as can be found in gold, silver, copper, as well as in other metals.

Uneven fracture: These are irregular and rough. This feature is very common in a lot of minerals though so it is not very useful when it comes to identifying them.

Tenacity is another characteristic that can be found in a lot of minerals and has to do with the resistance it has to being bent, broken, crushed or torn. The most essential classifications of tenacity are the following: 

Brittle: Minerals that are brittle can easily be broken or crushed down such as occurs with galena and sulfur.

Elastic: This is related to a mineral that goes back to its original form or shape such as talc.

Sectile: This consists of a mineral that can be cut with a knife such as talc and gypsum.

Malleable: This consists of minerals that can be pounded with a hammer for example and that can be reduced down to sheet such as with gold, silver and copper.

Ductile: There are certain malleable minerals that can be put through a small hole and that produce wire such as in the case of gold, silver and copper.

As can be seen from the previous list, a lot of minerals show more than one feature of tenacity and this is useful in helping us find some of the minerals that are a bit more difficult to recognize.