Earth Science Introduction to Minerals What are minerals

Earth Science Introduction to Minerals

What are minerals? �A mineral is a naturally occurring, homogeneous solid of definite chemical composition. It has a clear arrangement of its atoms and is formed by inorganic processes. �Most of these have specific atomic structures which can be discerned by studying the outward shape of the mineral (crystal structure). These reflect the arrangement of the atoms involved in forming the mineral.

Minerals, cont. �Minerals must occur naturally; coal, amber, obsidian are not minerals. �It has a chemical formula…this can have some variability due to impurities of other elements, which frequently impart different colors.

Minerals, cont. �Since each mineral has its own atomic make-up, each will also have its own collection of physical properties, unique to itself. �Properties: �Hardness (Moh’s scale, relative list) �Luster �Color �Shape �Density �Fracture or cleavage �Streak

Interesting Twists �Polymorphs: same composition, different structures �Graphite, Diamond �Quartz, Tridymite, Cristobalite, Coesite �Calcite, Aragonite �Pyrite, Marcasite �Isomorphs: same structure, different compostion �Olivine: series of Mg-Fe silicates �Calcite and Rhodochrosite: Ca or Mn carbonate �Apatite series: hydroxyl-or fluoro-phosphate of calcium

Some Familiar Minerals: Quartz Si. O 2

Pyrite: Fe. S 2

Calcite: Ca. CO 3

Halite: Na. Cl

Gypsum: Ca. SO 4 -2(H 2 O)

Beryl: Al 2 Be 3(Si 6 O 18)