Mineral Cleavage and Fractures
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.
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. 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. These can be found in obsidian and most quartz. Splintery or fibrous fracture: These are splinters or fibres 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 sulphur. 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.