Geo-211 Earth Materials Exam 2

crossed polarized light (XPL)

adding an additional polarizer called the analyzer to see different optical properties. this is generally on the top of the stage as a switch marked with an A

plane polarized light (PPL)

all microscopes have a polarizer below the stage on top of the light fixture, which only allows one direction of light to pass through

interference color

this is used to determine the birefringence of a mineral. in rotating the stage until it is furthest from extinction, at its brightest color. you choose the color near the center

birefringence

the property of some minerals that causes light to split into two rays when it passes through them. these typically show up in crystals that are hexagonal, tetragonal, and trigonal, which as uniaxial

pleochroism

some minerals will change color when the stage is rotated under PPL. it either is or isn’t and you always say what color it presents

relief

this is how distinct the mineral looks from the surroundings, and we generally look at the edges of a mineral to determine this

extinction

minerals that are not always black in XPL will typically go black every 90 degrees and we can measure the angles at which they go black.

opaque

metallic minerals are most often this. they will be solidly black in PPL or XPL.

interference figure

a figure observed with a conoscope when a section of a doubly refracting crystal is in the path traversed by convergent plane-polarized light

uniaxial

This will be a plus sign when observing the interference figure

biaxial

this will be curves at certain angles from 0 to 90 degrees when observing the interference figure

silicate

based on silicate tetrahedra (70-80% of our minerals). quartz SiO2- if there’s silicate in a mineral, it’s a silicate mineral

sulfate

sulfuric acid salts such as Barite and Gypsum

phosphate

phosphoric acid salts like Apatite

oxide

metal bonded to O2 like Cuprite

halide

contain halogen elements such as Cl, Br, F, I like Fluorite

carbonate

CO3 based like Calcite

native element

pure elements in solid form like Gold (Au)

tectosilicate

all SiO4 bonded to one another- Framework Silicates

phyllosilicate

basically Cyclo bonded together to form a flat regularly repeating structure (mica’s)

chain (ino-) silicate

a chain (single/double) of SiO4. each sharing two O with other tetrahedra- pryoxene or amphibole

nesosilicate

one SiO4 bonded to other elements

cyclosilicate

six SiO4 bonded in a ring form Si6O18

sorosilicate

two SiO4 bonded to form Si2O7 then bonded to other oxygen (sharing oxygen, which means one less)

how do we classify minerals based on composition

subclassify them based on the arrangement of tetrahedra relative to other elements

list common minerals for each subclassification of silicates

Nesosilicates: Forsterite, Fayalite, Kyanite/Andalusite/Sillimanite, Topaz. Sorosilicate’s: Epidote. Inosilicates (single-chain): pyroxenes (enstatite, ferrosilite, pigeonite, diopside, augite). Inosilicates (double-chain): amphiboles (hornblende, glaucophane). Cyclosilicates: Beryl, Tourmaline. Phyllosilicates: Talc, Illite, Chlorite, Biotite, Muscovite. Tectosilicates: Microcline, orthoclase, albite, andesine, labradorite, anorthite.

define plagioclase feldspar

two main endmembers: anorthite- Ca rich endmember (what moon is mostly made of), albite- Na rich endmember. Solid Solutions: Oligoclase, Andesine, Labradorite, Bytownite.

define alkali feldspar

Pure alkali polymorphs: orthoclase (monoclinic) and microcline (triclinic). mixed alkali with albite polymorphs: sanidine (monoclinic) and anorthoclase (triclinic). Unusual feldspars: celsian, hyalophane, buddingtonite.

define hydrolysis

the chemical breakdown of a compound and transformation of one mineral into another due to reaction with water

define ternary diagrams

we use a ternary diagram to talk about 3 component compositions

define QAPF diagram

we used a special stacked ternary diagram to talk about Igneous Rocks in particular. this is mostly for felsic and intermediate rocks. Q- quartz, A- alkali feldspar, P- plagioclase feldspar, F- feldspathoid

define biotite

microcline: tetra, sheet (brownish color)

define muscovite

define phlogopite

define kaolinite

1:2 (T-O)

define talc

1:2 (T-O-T)

define tetrahedra

consists of four oxygen atoms arranged as close as they can get around a central silicon atom

define octahedra

a three-dimensional geometric shape with 8 triangular faces

define T-O-T

Tetrahedra- octahedra- tetrahedra (one octahedral sheet bonded between two tetrahedra)

define T-O

tetrahedra- octahedra (one octahedral sheet with a tetrahedral sheet bonded on top

define dioctahedral

octahedra can arrange themselves so they have 2 or 3 positions filled, this essentially looks like having 3 vs. 6 octahedra surrounding the first one. this is typically Al

define trioctahedral

octahedra can arrange themselves so they have 2 or 3 positions filled, this essentially looks like having 3 vs. 6 octahedra surrounding the first one. this is typically Fe and Mg and is more densely packed

define interlayer

Between the layers of tetrahedra and octahedra, they may have “interlayers” composed of Na, Ca, K, and even Li

explain the types of sheet silicate layer arrangements (T-O-T and T-O)

T-O: if we take each base octahedral layer and replace 2 of the OH ions with O, we will bond with a tetrahedral sheet. if it’s a tri- containing Mg+2, we get lizardite. if it’s di- containing Al+3, we get Kaolinite. this leads to a T-O structure where each layer is bonded to the top/bottom of other T-O layers by Van der Waals bonds

T-O-T: if 2 of the OH ions in the octahedral layer are replaced by O, they can bond with another tetrahedral layer. this builds the trioctahedral phyllosilicate talc or the dioctahedral pyrophyllite. this becomes a T-O-T layer that can bond to another T-O-T layers by weak Van der Waals bonds

discuss the changes in physical properties based on layer arrangements

adding Al+3 causes an excess -1 charge in each TOT layer. replacing 2 more Si+4 ions with Al+3 ions results in an excess -2 charge in a TOT layer

discuss the shrink swell ability of expanding clays and why it happens

we know that mud cracks form as soil dries, this is due to the expanding clays shrinking as the moisture is removed.

define pyroxene

pyroxenes are single chain silicates. these can be divided into several groups based on chemistry and crystallography.

define amphibole

amphiboles are double chain silicates.

define pyroxenoid

these are similar to pyroxenes with slightly different structures. the Ca in this case can’t fit where it would normally go in a normal pyroxene. this changes the structure and properties of the mineral. it means the chain is less symmetrical and “twists”

define enstatite

orthopyroxene: MgSiO3. moderate relief, transparent in PPL, grey to white in XPL

define ferrosilite

OPX: FeSiO3, moderate relief, transparent in PPL, grey to white in XPL

define diopside

CPX:

define augite

CPX:

define actinolite

define tremolite

define cummingtonite

define glaucophane

differentiate between orthopyroxene, clinopyroxene, pyroxenoids, and amphiboles in thin section

OPX: moderate relief, transparent in PPL, grey to white in XPL. CPX: high relief, transparent to slightly brown in PPL, higher birefringence than OPX, second order colors and may display twinning. amphiboles:

what are the structural differences between pyroxenes, pyroxenoids, and amphiboles

define forsterite

define fayalite

define pryope

d

efine almandine

define kyanite

define sillimanite

define andalusite

define staurolite

explain how we identify different nesosilicates

discuss polymorphism of Kyanite/Sillimanite/Andalusite

how do you identify that a mineral is isotropic like garnet

these are minerals that are the same in all directions. in PPL they appear clear but in PPL they are always black

define beryl

describe why cyclosilicates are typically hexagonal crystal system

define calcite

define aragonite

de

define azurite

de

define malachite

explain differences between calcite and aragonite

discuss compositional similarities between minerals discussed so far in this course

define phosphate minerals

define apatite

define corundum

de

define rutile

define spinel

define brucite

define gibbsite

define bauxite

define geothite

why are hydroxide minerals softer than oxides?

describe where and how must hydroxides form

define/identify halogen

define fluroite

d

define halite

define sylvite

why are halide minerals often water soluble

where do most halide minerals form

define barite

define celestite

define gypsum board

discuss environments where sulfates are likely to form

define galena