Chapter 2-Minerals and Crystals

                      Physical Geology Illustrated Vocabulary  
Cochise College                                                     
Geology Home Page 
Roger Weller, geology instructor  
copyright 2018-Roger Weller
last edited: 3/22/18

calcite cleavage

Chapter 2


-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



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

-agate from Africa 

-agate from Lake Superior 

-red banded agate 
-agate-Opal's Pals



-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 


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




-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 



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

-barite crystal 

-barite rose 



-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 


-varieties of beryl 


-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.



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

-botryoidal azurite 

-botryoidal malachite 

-botryoidal hematite 

-botryoidal siderite 
-botryoidal marcasite 
-botryoidal goethite



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

-blue lace agate cabochon 

-fire agate cabochon 


-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


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.



-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 



-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 



-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 


-is a metallic element with a reddish color

-copper crystals 

-copper from Michigan 

-copper sheet 



-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.

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



-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
-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



-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 



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



-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 



-is a mineral with the composition of calcium magnesium carbonate;  
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 



-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 


-many varieties of feldspar 



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



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



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



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

-toothpaste with fluoride



-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 


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



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



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

-black obsidian



-is a metallic element with a bright yellow color.

-gold in quartz 
-gold nuggets 



-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 


-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


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



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

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


inorganic compound

-is a chemical compound that does not contain carbon.



-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.


-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).

lab created

-is a synonym for manmade or synthetic.

-lab created rubies 



-is a hydrated , yellow-brown iron oxide.




-refers to the surface appearance of a material.

-chrysotile, silky 

-galena and fluorite, metallic vs. non-metallic 

-stibnite, metallic 

-rose quartz, vitreous   



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

-magnetite, lodestone 



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

-magnetite, lodestone 



-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 




-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



-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.












naturally occurring

-means that the substance is not manmade.


non-metallic luster

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






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

-boulder opal 

-Nevada fire opal 



-means that no light can pass through the material.

-copper crystals 




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



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.







-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 



-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 



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



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

-faceted rubies 
-ruby crystal 
-star rubies 



-is the mineral halite, sodium chloride.

-views of halite 



- 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



-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.




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

-selenite cleavage 

-selenite crystal 



-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.







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



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



-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.



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).



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

-hematite streak 

-limonite streak 



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

-sulfur crystals from Michigan 

-sulfur, conchoidal fracture 
-sulfur, drusy 



-is a term that means manmade or lab created.

-synthetic rubies 

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



-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

-white talc 
-talc hardness


-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

-golden topaz crystals 

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


-is the ability to resist being broken.



-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



-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 

-really transparent selenite



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



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


vitreous luster

-is a glassy luster.

-rose quartz 

-black obsidian