Mineralogy Definitions

Tectosilicates

3D framework of tetrahedra All corners are shared with other tetrahedra in order to build a framework. The angle between the tetrahedra and the substitution of cations allow for different minerals of framework. SiOO ratio of 1-2

Layers of Cations C.

A simple layer of ions, normally potassium.

Nesosilicates

Isolated Tetrahedra No corner sharing with other tetrahedra Sio4 with a ratio of 1-4. Garnet is an example of this

Sorosilicate

Isolated pairs of tetrahedra Two bonded tetrahedra, one corner shared between them, but no other corners shared with other tetrahedra. Si2O7 with a ratio of 2-7. Epidote is an example.

Cyclosilicate

Isolated rings of tetrahedra 2 corners are shared with other tetrahedra in the ring, with no other bonding between them. A Si-O ratio of 1-3. The silica rings are staked but not bonded.

Octahedral Sheet O.

Bonded together by edge sharing, bonded to oxygen or OH. Dioctahedral or Trioctahedral

Prehnite

Ca2Al(AlSi4O10)(OH). It is a orthorhombic inosilicate made up of a complex chain of tetrahedra with cation and octahedra sites. It is also a common low grade metamorphic rock.

Microcrystalline Quartz

Made up of intergrown quartz crystals. Sometimes they are lined up, and other times they are not.

Tetrahedra Sheet T.

Sheet of tetrahedra at the core with Si or Al+Si

Phyllosilicate

Sheets of Tetrahedra 3 corners are shared with other tetrahedra to build sheets. Si2O5 or Si4O10 with a ratio of 2-5

Inosilicate

Single or double chains of tetrahedra 2 corners are shared with other tetrahedra in a single chain. Si2O6 with a ratio of 1-3 2-3 corners are shared with other tetrahedra, depending on where they are in the chain. Si8O22 with a ratio of 4-11

T. O. C.

Tetrahedra Sheet Octahedral Sheet Layers of Cation

Crystalline Quartz

These are still referred to as quartz and have the same composition. The difference is the color of the quartz. These differences come from impurities.

Al2SiO5 Polymorphs

These polymorphs are nesosilicates, there crystal structures differ in both the types and arrangement of the coordination sites.

Exsolution:

With decreasing temperature, the cation site "collapses" If its Na, then it becomes disordered, causing stress. With a mix of Na and Ca. Not all K feldspars have exsolution lamellae, but if there is enough Na, exsolution will create alternating zones of K and Na zones.

Olivine

a nesosilicate with isolated silica tetrahedra. The two coon olivine minerals are very common in mafic and ultramafic rocks.

Amphibole

double chain inosilicate. It is very similar to pyroxene, but has more cation sites and double chains of tetrahedra. The double chains of tetrahedra are bonded to the octahedra sites, with quarter sharing between the two, this being done through edge sharing.

Garnet

isometric nesosilicate with four primary end member minerals that form from a single solid solution.

Staurolite

monoclinic nesosilicate with the chemical formula Fe2Al9O6(SiO4)4(OH)4

Chloritoid

monoclinic nesosilicate with the chemical formula of (Fe,Mg)2(Al,Fe)Al3O2(SiO4)2(OH)4. It is a nesosilicate that has a semi-layered structure that is very similar to phyllosilicates. The octahedral sheets are held together by a single isolated tetrahedra.

Epidote

monoclinic sorosilicate with the chemical formula Ca2Al2(Al,Fe)(Si2O7)(SiO4)O OH. It is a common low grade metamorphic rock.

Cordierite

orthorhombic cyclosilicate with the chemical formula (Fe,Mg)2Al3AlSi5O18. It is a cyclosilicate with tetrahedra rings connected by octahedra sites.

Ternary Diagrams

used to plot mineral composition data. They have three axis that have three variables present.