Chapter 2-Minerals and Crystals

                      Physical Geology Illustrated Vocabulary  
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MINERALS and CRYSTALS
Roger Weller, geology instructor
wellerr@cochise.edu  
copyright 2018-Roger Weller
last edited: 3/22/18
   


calcite cleavage

Chapter 2

acicular

-is a needle-like arrangement of crystals; often applied to the
description of very fine, radiating, hair-like crystals.

-acicular cuprite, often called chalcotrichite

-acicular malachite 

 

adamantine luster

-is an extremely shiny surface, such as a diamond. 
This type of luster is shinier than glass (vitreous) luster.

-diamonds from Arkansas

-diamonds, natural

 

agate

-is a gem variety of cryptocrystalline quartz; usually banded.

-agate from Africa 

-agate from Lake Superior 

-red banded agate 
-agate-Opal's Pals

 

apatite

-is a mineral consisting of calcium phosphate.  This mineral has a hardness of 5 and resembles
many other minerals because of its wide range of colors.  It is the same mineral that your teeth
are made of.

-green apatite 
 

asbestos

-is a term that applies to several minerals that form long, hair like fibers.  It has been used for
insulation and fire-proof cloth.

-chrysotile 

 

azurite

-is a bright blue mineral; a basic copper carbonate.  This mineral is often found in the oxidized
zone above a copper sulfide deposit.
-drusy azurite 

-bright blue azurite 
-botryoidal azurite 
-azurite crystals on malachite 

 

barite

-is a mineral made of barium sulfate, distinguished by its high density of 4.3 to 4.6.

-barite crystal 

-barite rose 

 

beryl

-a mineral that commonly forms hexagonal prisms capped with a flat top (basal pinacoid). 
Beryl has the composition of beryllium aluminum silicate.

-common beryl 

-barrel-shaped crystals of beryl 

-aquamarine 

-varieties of beryl 
 

birthstone

-is a gemstone associated with the month in which a person is born. 
A birthstone is reputed to possess special powers by gem dealers trying to talk customers into
buying the gem.

 

botryoidal

-is a surface structure that resembles a bunch of grapes.

-botryoidal azurite 

-botryoidal malachite 

-botryoidal hematite 

-botryoidal siderite 
-botryoidal marcasite 
-botryoidal goethite

 

cabochon

-is a gemstone, usually translucent, that is cut and polished with a rounded surface.

-blue lace agate cabochon 

-fire agate cabochon 
 

calcite

-is a very common mineral with three directions of cleavage, hardness 3 on Mohs scale, and a
composition of calcium carbonate. In the form of a rock, if it is called limestone and if it has
undergone metamorphism, it is marble.

-calcite varieties
 

carat

is a measurement of the weight (mass) of a gemstone; 0.2 grams.

-2 carat white diamond 

chalky luster

-is a very dull, powdery surface appearance of a material.

-kaolinite clay 
-calcite, variety chalk
 

chemical compound

-consists of chemical elements combined together in a fixed ratio.

 

chemical property

-is the identification of a mineral through the use of chemicals. 
For example, hydrochloric acid applied to the mineral
calcite produces bubbles of carbon dioxide.

 

clay

-can either refer to the tiniest particle size (submicroscopic particles) or it can apply
to a class of silicate minerals that only produce crystals in the submicroscopic range
(clay minerals).

-kaolinite clay 

 

cleavage

-is the tendency of a crystallized mineral to break along flat planes aligned with a zone of
weak bonding within the crystalline structure of the mineral.

-fluorite, multicolored cleavages 

-calcite cleavage 
-halite cleavage 

 

color

-is composed of the frequencies of light reflected off of the surface of a material or transmitted
through it when the material is exposed to white light.

-fluorite, purple 
-fluorite, multicolored cleavages 

-watermelon tourmaline 

-red, white and blue agate 

 

conchoidal fracture

-The material breaks in a shell-like pattern.

-quartz, conchoidal fracture 

-sulfur, conchoidal fracture 
 

copper

-is a metallic element with a reddish color

-copper crystals 

-copper from Michigan 

-copper sheet 

 

corundum

-is a mineral consisting of aluminum oxide; the mineral next in hardness to a diamond.

-rubies and sapphires 

-ruby crystal 

-common corundum 

 

covalent bond

-is a type of bonding in chemicals where electron pairs are shared between adjacent atoms.

cryptocrystalline
-refers to a material consisting of extremely small crystals, often sub-microscopic.
-cryptocrystalline

 

crystal

-is a mineral whose internal, geometrical repeating pattern of atoms is consistent throughout
the entire structure; the object may also have flat surfaces (crystal faces) that reflect the
internal arrangement of atoms.
-quartz crystals 
-calcite crystals   
 

crystal face

-is one of the flat surfaces on a crystal.

-pyrite crystals 

-galena and fluorite crystals 

-garnet crystal 
-quartz crystal 

 

crystalline structure

-is where the atoms within a crystal are all aligned in a geometrical, repeating three dimensional
pattern.
-crystalline structure 
-crystalline structure-halite
-crystalline structure-calcite
-crystalline structure-diamond
-crystalline structure-graphite
 

cubic zirconia

-is a synthetic material made of zirconium oxide that is used in jewelry because it has optical
properties similar to diamond; also nicknamed CZ.
-cubic zirconia

 

cuprite

-is a mineral whose composition is copper oxide.  Cuprite varies from deep red in finely
crystallized forms
to a dark, semi metallic luster in massive forms.
-cuprite-variety chalcotrichite 
-red crystals of cuprite 
-massive cuprite 

 

density

-is a measurement of the mass of an object compared to its volume; often expressed in terms of
grams per cubic centimeter.
-density

 

diamond

-is the hardest known mineral; made of just carbon.

-diamonds from Arkansas 

-2 carat white diamond 

-faceted diamonds 
 

dogtooth spar (calcite)

-is a crystalline form of the mineral calcite that resembles a dog's canine tooth. 
The scientific term for this shape is scalendohedron.

-calcite, dogtooth spar-1 

-calcite, dogtooth spar-2 

-calcite-dogtooth spar-3 
-calcite-dogtooth spar-4 

-calcite-dogtoothspar
 

dolomite

-is a mineral with the composition of calcium magnesium carbonate;  
it
fizzes slower with hydrochloric acid than calcite.

-dolomite crystals 

 

dull luster

-is a surface appearance that is the opposite of shiny; a dull surface has no highlights or sparkles.

-limonite, dull luster 
-calcite-variety chalk 

  

emerald

-is a green form of the mineral beryl; one of the most expensive of all precious gemstones.

-emerald crystal 

-faceted emeralds 

 

faceted gemstone

-is a transparent gemstone that has been shaped and polished with flat surfaces.

-faceted amethyst 

-faceted aquamarine 
-faceted diamonds 
 

feldspar

-many varieties of feldspar 

 

flexible

-refers to a substance that is capable of being bent
-bent selenite 

 

fluorescence

-is the process in which a material absorbs ultraviolet light and then emits light in the visible
spectrum.
-The following photos are minerals viewed under ultraviolet light.
-fluorescent aragonite 
-fluorescent fluorite 
-fluorescent willemite 
-fluorescence

 

fluoridation

is the process of adding fluoride compounds drinking water to prevent dental decay.

 

fluoride

-is a chemical compound consisting of one or more elements combined with fluorine.

-toothpaste with fluoride

 

fluorite

-is a mineral with the composition of calcium fluoride.  Fluorite is number 4 on Mohs scale of
hardness; it is often distinguished by its four directions of cleavage.
-fluorite cleavage octahedrons 

-fluorite from Mexico 

-fluorite from Illinois 

 

fools' gold

-is a fanciful name for the mineral pyrite.  Early prospectors were often fooled by the yellow
metallic color of pyrite and thought that they had discovered real gold.

-pyrite crystals-1 

-pyrite crystals-2 

fracture

-is the way a material breaks.
-fracture-Opal's Pals

 

friability

-is the measure of how easy it is to crumble a material.
-friability

 

glass

-is a solid in which the atoms are are all in a chaotic distribution and not crystallized.

-black obsidian

 

gold

-is a metallic element with a bright yellow color.

-gold in quartz 
-gold nuggets 

 

gypsum

-is a soft mineral with the composition of hydrated calcium sulfate. 
This mineral is commercially baked to drive the water out of the chemical structure and then
ground to a fine powder to create Plaster of Paris.

-varieties of gypsum 
 

hardness

-is the ability of a material to scratch other materials or to be resistant to other materials trying
to scratch it.
-See: Mohs scale of hardness
 

heft

-is a crude measure of the density of a material by shaking the object with your hand

 

hematite

-is a reddish brown to dark, sub-metallic mineral consisting of iron oxide

-hematite, streak 
-hematite, botryoidal 
-hematite, specular 
-hematite

 

inorganic compound

-is a chemical compound that does not contain carbon.

 

ion

-is an atom or group of atoms with excess electrical charge, not electrically neutral.
-ion-Opal's Pals

 

ionic bond

-is a chemical bond that holds a material together by the electrostatic attraction of the ions that
compose the material.

 

karat
-is used to describe the purity of gold in a gold alloy.  Pure gold is 24 karat.
Gold jewelry is often 14 karat (14 k) or 10 karat (10 k).
-karat
 

lab created

-is a synonym for manmade or synthetic.

-lab created rubies 

 

limonite

-is a hydrated , yellow-brown iron oxide.

-limonite 

 

luster

-refers to the surface appearance of a material.

-chrysotile, silky 

-galena and fluorite, metallic vs. non-metallic 

-stibnite, metallic 

-rose quartz, vitreous   

 

magnetic

-is a physical property in which a material is attracted to a magnet.

-magnetite, lodestone 
-magnetic

 

magnetite

-is the most common occurring mineral that is attracted to a magnet. 
It is a black mineral made of iron oxide.

-magnetite, lodestone 

 

malachite

-is a green copper mineral having the composition of a basic copper carbonate. 
Pure, solid forms of this mineral are often used in jewelry.

-views of malachite
 

metallic luster

-is where the surface of the material reflects light like a metal.

-pyrite crystals 

-stibnite 

-chalcopyrite 
-bornite 
 

mica

-is mineral from a group of silicate minerals that have perfect one-directional cleavage and
peel in very thin layers.
-muscovite crystal 

-muscovite and biotite 

-varieties of mica 
-mica book

 

mineral

-is a material that must meet the following 5 criteria: (1) an element or a chemical compound,
(2) naturally occurring, (3)  a crystalline structure, (4) inorganic (no carbon) (exceptions are
carbonates and pure carbon), and (5) distinct physical properties.

 

Mohs scale of hardness

-is a series of ten minerals arranged in ascending order of hardness.

*10-diamond 

*9-corundum  

*8-topaz 

*7-quartz 

*6-feldspar   

*5-apatite   

*4-fluorite   

*3-calcite  

*2-gypsum  

*1-talc   

 

naturally occurring

-means that the substance is not manmade.

 

non-metallic luster

-is a broad array of surface appearances other than a metallic sheen.

-brucite 

-diopside 

-malachite 

 

opal

-is a mineraloid composed of silica and a variable amount of water.
-common opal 

-boulder opal 

-Nevada fire opal 

 

opaque

-means that no light can pass through the material.

-copper crystals 

-pyrite 

-opaque
 

peridot

-is the name of the gemstone variety of the mineral olivine.  It is usually yellow-green in color.

-peridot-1 

-peridot-2 
-peridot-3

phantom crystal
-is a clear crystal that shows its early development shape due to the earlier form being
partially covered by impurities.
-phantom amethyst crystal
-phantom crystal

 

precious gemstone

-are the most expensive gemstones such as ruby, sapphire, diamond, emerald, etc.

-rubies

-sapphires

-diamond 

-emerald 

 

pyrite

-is a brassy yellow metallic luster mineral consisting of iron sulfide. 
This mineral commonly crystallizes in the form of cubes or 12-sided pyritohedrons and is
also known as Fools' Gold.
-pyrite, cubes 

-pyrite, pyritohedron crystals 

 

quartz

-is one of the most common minerals on the Earth, consisting of silicon and oxygen. 
This mineral is number 7 on Mohs sale of hardness. 
Quartz occurs in many different forms and may be crystalline, cryptocrystalline, or massive.

-quartz, rock crystal 

-quartz, amethyst 

-quartz, smoky quartz 
-quartz, agate 
-quartz family 

 

rock

-is a solid, coherent mass of naturally occurring material made from one or more minerals.

 

ruby

-is red colored corundum, one of the most expensive gemstones.

-faceted rubies 
-ruby crystal 
-star rubies 

 

salt

-is the mineral halite, sodium chloride.

-views of halite 

 

sapphire

- is corundum that is colored in any hue with the exception of red. 
Red corundum, however, is called ruby. 
These gems can be colorless, pink, yellow, violet, green, black, etc.
The color most commonly associated with this gem is blue.
-faceted blue sapphires 

-faceted pale blue sapphires 

-yellow sapphires 
-pink sapphires
-mixed colors of sapphires

 

schiller

-is an optical effect, commonly observed with the mineral labradorite, where a play of colors
suddenly appear
when the specimen is oriented at a specific angle to a light source.

-labradorite-schiller 

 

selenite

-is a transparent and colorless form of the mineral gypsum.

-selenite cleavage 

-selenite crystal 

 

silica

-is a compound of silicon and oxygen; usually refers to the mineral quartz but may also refer
to opal.

-quartz, rock crystal 

-quartz, banded agate 

-common opal
-silica gel:  1  2 

 

silicate mineral

-is a mineral made of silicon and oxygen plus at least one more element.

-diopside 

-hornblende 

-kyanite 

-feldspar 

-lepidolite 

 

silica tetrahedron

-is the basic building block of silicate minerals. 
Each silicon atom is surrounded by four oxygen atoms in order to create the silica tetrahedron.
-silica tetrahedron

 

silicon

-is the element number 14; semi-metallic.  It does not occur naturally in its pure form on the surface
of the Earth.

-silicon-1
-silicon-2

-silicon-3
-silicon-4

silicone
-is a synthetic, man-made rubbery material is in caulking and breast implants.

 

silky luster

-is a surface appearance that resembles the shiny reflection off of a spool of thread.

-chrysotile 

 

specific gravity

-is the comparison of the density of a material with the density of water; usually expressed as a
decimal number greater than 1 (because rocks and minerals rarely float).

 

streak

-is the color of the powdered form of a mineral when it is rubbed against an unglazed, white 
porcelain
tile.

-hematite streak 

-limonite streak 

 

sulfur

-is a  lemon yellow, transparent to translucent element that burns in an oxygen atmosphere.

-sulfur crystals from Michigan 

-sulfur, conchoidal fracture 
-sulfur, drusy 

 

synthetic

-is a term that means manmade or lab created.

-synthetic rubies 

-synthetic opal 
-faceted synthetic stones
-all types of synthetic gemstones

 

talc

-is a metamorphic mineral, typically white or pink, that is extremely soft. 
This mineral is ground to a very fine powder and when perfume is added to it, it becomes talcum
powder.

-white talc 
-talc hardness

topaz

-is a complex silicate mineral often containing fluorine in its structure. 
This mineral is number 8 on Mohs scale of hardness and has one direction of perfect cleavage. 
It is a gemstone of many colors, but the blue varieties are artificially created by exposure to
radioactivity.

-golden topaz crystals 

-clear, colorless crystal of topaz 
-topaz crystals of various colors 
-large topaz crystal
-faceted blue topaz-irradiated 
 

toughness

-is the ability to resist being broken.
-toughness

 

translucent

-is an optical property of minerals where some light is transmitted through a material and there is a
cloudy appearance.

-translucent jade 
-polished labradorite

-polished moonstones
-translucent

 

transparent

-is the optical condition where light goes through the material without any distortion. 
Color may be present, but if the material were to be finished as a flat, polished slab, you could
read newsprint through it.

-quartz, rock crystal 

-selenite 
-really transparent selenite
-transparency

 

turquoise

-is a blue to green translucent gemstone consisting of a hydrated copper, aluminum phosphate.

-turquoise 

 

ultraviolet light

-is where light just outside of the normal visible spectrum, just past violet. 
This light with a shorter wavelength than violet light is responsible for sunburn on bright, sunny
days.

 

vitreous luster

-is a glassy luster.

-rose quartz 

-black obsidian

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