Lab 2 Chapter 1 Quiz

mineral fractures

a mineral fractures if it breaks along random, irregular surfaces. some minerals break only by fracturing while others both cleave and fracture.

mineral

a naturally occurring compound or chemical element made of atoms arranged in an orderly, repetitive pattern; both chemical composition and atomic arrangement characterize a mineral and determine its physical properties. the precise chemical composition and internal atomic architecture that define each mineral also directly determines its outward appearance and physical properties. Thus, in most cases, general appearance and a few easily determined physical properties are sufficient to identify the mineral

crystal

a solid, homogenous, orderly array of atoms and may be nearly any size important to determine whether you are looking at a single crystal with well developed crystal faces, a fragment of a crystal (which is still considered a crystal bc of its molecular arrangement), or a group of small, irregularly shaped intergrown crystals

streak plate

an unpolished piece of white porcelain on which the mineral is scratched

cleavage and cleavage planes

because the way in which a mineral breaks is determined by its chemical bonds, it can aid in mineral identification a mineral that exhibits *cleavage* consistently breaks, or cleaves, along parallel, flat surfaces called *cleavage planes*

luster

describes the appearance of a mineral when light is reflected from its surface (shiny/dull) most minerals have either a metallic luster (often w an opaque color) or nonmetallic luster (of any color) - note: many metallic minerals become dull when exposed to air so you must look at a recently broken part to determine its luster

several types of nonmetallic luster: -dull luster

earthy appearance caused by weak or diffuse reflection of light

directions of cleavage

ex) when NaCl (aka Halite) breaks, it breaks in 3 directions (3 perpendicular planes). Because there are 3 directions in which atom density is equal, halite has three *directions of cleavage*, each at 90 degrees to each other the number of cleavage directions and the angles between them are important in mineral identification bc they reflect underlying atomic structure

striations

plagiocase feldspar can be identified from potassium feldspar by the presence of very thin, parallel grooves called striations; the grooves are present on only one of the two sets of cleavages and are best seen with a hand lens

*guaranteed question on quiz* divergent plate boundary -what is it -features (4) *know these* -location example

plates moving apart features: volcanoes and ridges, mid-ocean ridges, new oceanic crust, low seismic activity locations: mid-atlantic (between US and europe around 0 longitude)

*guaranteed question on quiz* transform plate boundary -what is it -features (3) *know these* -location example

plates sliding next to each other features: shallow earthquakes, laterally displaced surface features (ex: messed up fences in CA), little to no volcanic activity ex) San Andreas fault in North American Pacific

determining hardness

run a sharp edge or point of a mineral with known hardness across a smooth face of the mineral to be tested, in a straight line pushing hard; brush off dust and see if a scratch remains

how can cleavage planes, as flat surfaces, be spotted by the naked eye?

simply by turning a sample in your hand until you see a single flash of reflected light from across the mineral surface

magnetism

some minerals are attracted to a hand magnet; magnetite, however, is the only common mineral that is strongly magnetic

crystal and mineral identification

some minerals commonly occur as well-developed crystals, and their crystal forms are diagnostic examples) quartz commonly has hexagonal prisms with pyramid-like shapes at the top pyrite occurs as cubes or as pyritohedrons (12 pentagonal faces) calcite occurs as rhombohedrons (6-sided forms that look like cubes squashed by pushing down on one of the corners)

fracture surfaces use in identification

some minerals fracture in a way that helps to identify them: ex) quartz has no cleavage but, like glass, it breaks along numerous, small smooth, curved surfaces called conchoidal fractures. other kinds of fractures have descriptive names such as fibrous, splintery, or irregular

acid

some minerals, especially carbonate minerals, react visibly with acid (often HCl is used); especially useful for identifying calcite and dolomite, which are both carbonate minerals

*guaranteed question on quiz* convergent plate boundary -what is it -features (4) *know these* -location example

two plates collide, one goes under the other or crumples (older/denser one goes is the one that subducts) features: mountains, low points (trench), high seismic activity (earthquakes), volcanoes often can have very old rock buried below location: along japan

which is more reliable: streak or color?

typically streak

minerals with 4-6 cleavage directions -frequency

uncommon; 4 cleavage planes can intersect to form an eight-sided octahedron (ex: fluorite has this octahedral cleavage) 6 cleavage directions intersect to form a dodecahedron (a 12 sided form with diamond shaped faces); ex) sphalerite has dodecahedral cleavage

color

useful but can be deceiving; color generally is diagnostic for minerals with a metallic luster

3 cleavage directions

with 3, minerals can be broken in the shape of a cube (makes sense bc it now has 3 dimensions: length, width, and depth) if the 3 cleavages intersect at 90 degrees : called a *cubic cleavage* . If the angles are not at 90 degrees it's called a *rhombohedral cleavage*

what do crystal faces often get mistaken for? How can they be distinguished?

for cleavage surfaces; 1) crystal faces are normally smooth whereas cleavage planes, though also smooth, commonly are broken in a steplike fashion 2) some crystal faces have fine grooves or ridges on their surfaces, whereas cleavage planes do not. (similar looking thin, parallel grooves called striations are seen on plagioclase cleavage surfaces but these features persist throughout the mineral and are not surficial 3) unless crystal faces happen to coincide with cleavage planes, the mineral will not break parallel to them

fracture surfaces (comparison to cleavage surfaces)

fracture surfaces can cut a mineral grain in any direction and are generally rough or irregular, rather than flat, and thus appear duller

thing commonly used in geology labs to be scratched

glass bc its easy to scratch on glass, its midway on the Mohs scale (a 5-5.5) and glass is inexpensive

several types of nonmetallic luster: -greasy luster -waxy luster -resinous luster

greasy luster: as though covered by oil waxy luster: like paraffin resinous luster: like resin or tree sap

prism, prismatic cleavage

intersecting cleavages may define an elongate geometric object called a *prism*; such minerals are said to have prismatic cleavage

cleavage quality -3 descriptions

is described as perfect, good, or poor perfect: break easily along flat surfaces and are easy to spot good: do not have well-defined cleavage planes and reflect less light poor: toughest to recognize but can be spotted by small flashes of light in certain positions

streak -what is it? -impact of metallic vs nonmetallic lusters

is the color of the mineral when finely powdered (may or may not be the same color as the mineral) more helpful for identifying minerals with metallic lusters bc those w nonmetallic lusters generally have a colorless or light colored streak that is not very diagnostic

hardness

is the resistance of a smooth surface to abrasion or scratching ; minerals in the Mohs Hardness Scale are used as standards for comparison

several types of nonmetallic luster: -pearly luster

like a pearl or the inside of a fresh clam shell

several types of nonmetallic luster: -vitreous luster

like that of glass (can be any color though)

minerals of the same hardness

may be able to scratch each other

numbers of cleavages

minerals have characteristic numbers of cleavages, determined by counting the number of cleavage surfaces that are NOT parallel to each other (see top of pg 6 for pic diagram)

basal cleavage

minerals with one cleavage

how is cleavage truly counted?

must be counted on just ONE mineral crystal, unlike the pics shown in the book which are used to illustrate cleavage

two cleavage directions -common angles

must be nonparallel; often involves one horizontal and one vertical common angles are either both at 90 degress or at 60 and 120

mineraloids

naturally occurring substances that have characteristic chemical compositions, but are amorphous-that is their atoms are not arranged in regular patterns (ex: opal)