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MINERALS
Lesson 3 - Page 1

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FAMILY OF MINERALS   

 The chemical composition of a mineral determines the overall geometric arrangements of that mineral. How the atoms bond with each other determines other properties including crystal shape, cleavage, behavior of light, and hardness.

Chemical families are divided into classes depending on the anion or positive radical that is part of their chemical formula. A positive radical is a combination of elements that have a positive charge and is a prominent part of the chemical formula that makes up the mineral. You can think of a "family" with the same last name. For example feldspar has a radical of Si3O8 and mica has a radical of Si3O10. Both have silicon and oxygen in their family name, so they both belong to the silicate family.

Chemical families help to group minerals to look for similar properties. For example, "carbonatesí include the radical "CO3 " which reacts with acids to produce carbon dioxide. Minerals like calcite and azurite will produce a "fizzing" as carbon dioxide bubbles are released when acid like HCl is dropped on the mineral. Many oxides will react with the atmosphere and will "rust." Limonite belongs to the oxide  family and has a characteristic rust color.

We will look at 6 positive radials in our chemical family chart including oxides, sulfides, sulfates, carbonates, silicates, borates, and halides. There are a few other groups of chemical families that we have not included in this chart because they are not common minerals.


Feldspar - a silicate


Mica - a silicate

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