Rock and Minerals

Rocks

rock- an aggreagste of two or more minerals

- there are osme rocks that are composed of one mineral

- there are also a few rocks composed of non-mineral matter

Minerals

mineral- is defined as being

-naturally occurring

- usually inorgainc

- homogeneous solid

- with a definite ( but usually not fixed) chemical composition and 

- with anorders atomic arrangement 

Mineralogy- as a scince is relativley recent

- early humans used natural pigments of hematite and manganese in cave paintings and flint was higly prized

- tomb paintings in the Nile 5,000 years agom show people weighing malachite and percious metals, smelting mineral ores, and makeing lapis lazuli and emerald gems

- the Greek philosopher Theophrastus (372-287 b.c) recorded the frist written work (on stone) on minerals.

1556- german physicist Georgius Agricola published De Re Metallica. Many believe this documnet signals the emergence of mineralogy as a science,

1669- Nicolaus Steno published results of his studies of quartz crystals-- Steno's Law of Constant Angles

1784 - Rene J. Hauy showed that crystals were " built" by stacking together "tiny identical building blocks"

1779 - 1848 Jons Jacob Berzelius studied minerla chemistry and devloped chemical classifaction of minerals; discvered Si, Se, Th, Ce.

1824 - Austrain mineralogist Frederich Mohs devised a series of 10 common minerals that may be sused as a mineral baseline for comparing hardenss of any mineral

The Moh's Scale of Hardness

1= softest  10= Hardes

1 Talc 

2 Gypsum

3 Calcite

4 Florite

5 Apatite

6 Orthoclase

7 Qartz

8 Topaz

9 Corundum

10 Diamond

Crystals

- a crystal is a homogeneous solid possessing long-range, three- dimensional internal order

7 Crystal Systems

Triclinic - 3 unequal axes, all intersecting at oblique angles

Monoclinic - 3 unequal axes, two are perpendicular while the third is at an angle other then 90 to the other two

Orthorhomic - mutually perpendiular axes all of different lengths

Tetragonal - 3 mutually perpendicular axes, two of which ( horizontal) are equal length, but the vertical axis is shorter or longer

Hesagonal-- Trigonal 0 3 unegual axes, tow of which intersect at 120

Hexagonal - 4 axes, 3 equal horizontal axes intersecting at 120, the foruth ( vertical) is of diferent length and perpendicular to the planes of the other 3

Isometric ( cubic) - 3 mutally perpendicualr axes of equal lengths

Crystal Forms

euhedral- a crystalline solid with wellformed faces

subhedral- a crystalline solid with imperfectly developed faces

Anhdral- a crystalline solid without faces

Microcystalline- the crysrtalline nature can only be determined with the aid of a microscope

Cryptocrystalline - the crystalline nature can only be detected using X-ray diffeaction

Amorphous- a substacne that lacks ordered internal atomic arrangement

Crystal habit- " the genral shapes of crystal... habit is controlled by ther environment in which crystals grow... only rarely do crystals present an ideal geometrical shape"

" Cleavage is the tendency of minerals to break parrellel to atomic planes"

Cyrstallization

" the process by which matter becomes crystalline, from a gaseous, fluid, or dispersed state"

- Crystalline: having a regular molecular structure; os ,or pertaining to the natuire of a crysrtal

there are 3 very general modes of crystal formation

1 crystallization from a solution

2 due to temperature/pressure changes

3 forming from a melt

Varistions in Minerals

Both the chemical compostion and form ( stucture) of mineral can vary widely within one general mineral type

Compositional variations: ions of similar size may substitute into the mineral's internal framework

Stuctural Variations: two minerals with the same chemical compsition with different internal ordering ( and thus differenet external forms) are called polymorphs

Mineral Classes

Silicates 

all silcate minerals contain silica (Si) and oxygen (O) bound together in the form of the " silica tetrahedron" [ four O2- anions covalenty bonded to one Si4+ cations]

Silicate Structures 

- Nesosilicates: independent

- Sorosilicates: double tetrahedra

- Insilicates: single chain/ double chain

- Phyllosilicates: sheet

- Cyclosilicates: ring structure

- Tectoslilicates: 3-D framework

Dark Silicates

typically, dark silicates are ferromagnesian

- Olivine group- a dark greenish, high temperature mineral often associated with mantle conditions

- Puroxene group- a common mineral type in basalt

- Amphibloe group- a type of[ical merianl type in intrusive ingeous and metamorphic rocks

- Biotite- ndark mica

- Garnet- a nesosilicate common in metamorphic and intrusive ingeous rocks