Gems And Their Physical Properties

Front 1

Define unit cell

Back 1

The smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral.

Front 2

Under the right conditions, and when all the right elements are present in the correct concentrations, atoms come together to form__________

Back 2

Gem crystals

Front 3

A solution that's highly saturated in nutrients produces

Back 3

Many small crystals

Front 4

Define aggregate

Back 4

A mass of many small crystals formed by nutrient saturated solution or rapid cooling

Front 5

Rapid cooling produces what type of crystals

Back 5

Many small

Front 6

What type of crystals does basalt contain and why

Back 6

Many small due to rapid cooling

Front 7

Slow cooling produces what type of crystals

Back 7

Larger single crystals

Front 8

Which has larger crystals: basalt or granite. Why?

Back 8

Granite due to slower cooling

Front 9

Solution with a lower concentration of nutrients yields

Back 9

Larger single crystals

Front 10

What is the best example of fewer crystallization centers and larger single crystals

Back 10

Pegmatites

Front 11

Gem minerals that are made iPod sense, closely packed masses of tiny randomly oriented crystals are called

Back 11

Aggregates

Front 12

Name two types of individual crystals in aggregates

Back 12

Microcrystalline and Cryptocrystalline

Front 13

Define Microcyrstalline

Back 13

An aggregate made up of individual crystals visible under magnification

Front 14

Name 3 microcrystalline gems

Back 14

Nephrite, jadeite and quartzite

Front 15

Define Cryptocrystalline

Back 15

An aggregate made up of individual crystals detectable only under very high magnification

Front 16

Name 2 cryptocrystalline gems

Back 16

Chalcedony and turquoise

Front 17

Explain crystallization process

Back 17

Atoms come closer and closer together until they finally form connection bonds

Front 18

How are brick structures like crystal structures

Back 18

They are repetitions of tiny, identical units that are stacked to give shape and structure.

Front 19

Differences between gems are due to differences in the ______ and _____ of their unit cells

Back 19

Proportion and Symmetry

Front 20

Crystalline minerals are classified into 7 crystal systems depending on _________

Back 20

The symmetry of their unit cells.

Front 21

Name the 7 crystal systems

Back 21

Cubic, Tetragonal, Hexagonal, Trigonal, Orthorhombic, Monoclinic and Triclinic

Front 22

Which is the most symmetrical of the crystal systems

Back 22

Cubic

Front 23

Which is the least symmetrical of the crystal systems

Back 23

Triclinic

Front 24

4 Cubic gems

Back 24

Diamond, spinel, garnet, fluorite

Front 25

Name a Tetragonal gem

Back 25

Zircon

Front 26

2 Hexagonal gems

Back 26

Apatite, Beryl

Front 27

3 Trigonal (Rhombohedral) gems

Back 27

Corundum, quartz, tourmaline

Front 28

5 Orthorhombic gems

Back 28

topaz, ioite, tanzanite, chrysoberyl and peridot

Front 29

Name 2 monoclinic gems

Back 29

Kunzite and moonstone

Front 30

Name 2 Triclinic gems

Back 30

Amazonite and rhodonite

Front 31

Spinel's typical shape

Back 31

cubic-system crystal: it's top is an eight-sided octahedron

Front 32

Garnet's typical shape

Back 32

rhombic dodecahedron with twelve equal diamond shaped faces

Front 33

Zircon's typical shape

Back 33

Tetragonal system: They feature four rectangular sides and a pyramid shaped top with four triangular faces that meet in a point

Front 34

Beryl's typical shape

Back 34

hexagonal crystal system: six flat faces and columnar shape. Elongated in one direction.

Front 35

Tourmaline's typical shape

Back 35

Trigonal system: Long and slender with vertical grooves parallel to their length

Front 36

Topaz's usual shape

Back 36

Orthorhombic system: Usually elongated with obvious vertical grooves with triangular faces that give the top a chisel shape

Front 37

Kunzite's typical shape

Back 37

Monoclinic system: asymmetrical form with vertical grooves often capped by angled flat faces that form an irregular surface

Front 38

Most rock and mineral crystals are formed from the 8 most abundant chemical elements in the earth's crust. Name them.

Back 38

Oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium

Front 39

Which rare element is responsible for emerald green and ruby red

Back 39

Chromium

Front 40

What does quartz require to form

Back 40

oxygen and silicon

Front 41

What does an emerald require to form (Elements)

Back 41

Silicon, oxygen, aluminum, beryllium and chromium

Front 42

Define Twinning

Back 42

change in a gem's crystal direction during or after growth

Front 43

Define twinning plane

Back 43

Location of a change in crystal growth direction

Front 44

Primary twinning

Back 44

when twinning happens during a crystal's original growth period

Front 45

In one type of primary twinning, the twinned crystals look like one half is a mirror image, these are known as ____ and are most often seen in ____gems

Back 45

contact twins seen most often in spinel and are sometimes called spinel twins.

Front 46

What type of twin is this

Back 46

contact twin, one side is a mirror image of the other.

Front 47

Define penetration twinning

Back 47

when 2 crystals look as though 2 crystals have grown through one another

Front 48

2 gems that show penetration twinning

Back 48

Fluorite and quartz

Front 49

type of twinning

Back 49

penetration

Front 50

Define cyclic twinning

Back 50

occurs when the twinning planes aren't parallel and results in a wheel shaped crystal

Front 51

type of twinning

Back 51

cyclic

Front 52

What causes secondary twinning

Back 52

changes in environment after the crystal has formed, such as cooling temperatures or the pressure of metamorphism

Front 53

define polysynthetic-lamellar-twins

Back 53

the boundaries between the twinned crystals are parallel.

Front 54

Gem materials that are commonly twinned: (5)

Back 54

quartz, spinel, corundum, feldspar and chrysoberyl

Front 55

Define inclusion

Back 55

A characteristic enclosed within a gemstone, or reaching its surface from the interior

Front 56

Define liquid inclusion

Back 56

small pocket in a gem that's filled with fluids and sometimes gas bubbles and tiny crystals

Front 57

Which gems are prone to include liquid inclusions (3)

Back 57

Topaz, emerald and amethyst

Front 58

define two-phase inclusion

Back 58

A hollow cavity in a gem, usually filled with a liquid and a gas

Front 59

Define three-phase inclusion

Back 59

A hollow cavity in a gem filled with a liquid, a gas, and one or more crystals.

Front 60

Which gem has characteristic three-phase inclusions that are key to their identification

Back 60

Columbian emeralds

Front 61

define trace elements

Back 61

Atoms in a gem that aren't part of its essential chemical composition.

Front 62

growth tubes are common in which gem

Back 62

tourmaline

Front 63

what effect can growth tubes produce if cut correctly

Back 63

cat's eye

Front 64

which trace elements cause sapphire's blue color

Back 64

Iron and titanium

Front 65

Define habit

Back 65

The characteristic external crystal shape or form of a mineral

Front 66

crystals without obvious crystal faces are described as

Back 66

anhedral

Front 67

Describe this rough

Back 67

Ruby: Squat flattened crystals with triangular surface features on the top.

Front 68

describe this rough

Back 68

sapphire: two sets of six triangular faces joined back to back. Linear markings run horizontally across the crystal faces.

Front 69

Describe this rough and where commonly found

Back 69

Chrysoberyl twins, star shaped. Common in gem gravels of Brazil

Front 70

Describe this rough

Back 70

Imperial topaz: Diamond shaped cross section, vertically grooved sides and a chisel-shaped top

Front 71

Describe this rough and what they look like in gem gravel

Back 71

Garnet: Occurs as 12-sided (dodecahedral) crystals. In gem gravel they're mostly worn to a rounded ball-like shape.

Front 72

Define tubular & give an example

Back 72

Squat and flat. Corundum crystals.

Front 73

Define prism or prismatic & give an example

Back 73

Columnar, with 3, 4, 6, 8 or 12 parallel faces. Many aquamarine and tourmaline crystals.

Front 74

Define Euhedral and give an example

Back 74

Well formed with sharp crystal faces. Most gems from pegmatite pockets.

Front 75

Define striations (both types) and give examples of each

Back 75

Growth marks on a crystal. Horizontal (quartz, corundum) or vertical (tourmaline, topaz)

Front 76

define pyramid

Back 76

shape with equal triangular faces that meet in a point

Front 77

Define bipyramid and give an example.

Back 77

Shape with two pyramids, back to back. Seen in sapphires.

Front 78

define density

Back 78

how heavy an object is in relation to size

Front 79

define specific gravity (SG)

Back 79

Ratio of the weight of a material to the weight of an equal volume of water

Front 80

define durability

Back 80

a gemstone's ability to withstand wear, heat and chemicals

Front 81

define hardness

Back 81

how well a gemstone resists scratches

Front 82

define toughness

Back 82

how well a gemstone resists breaking and chipping

Front 83

what does the Mohs scale measure?

Back 83

A gems hardness

Front 84

a gem crystal's hardness is directly related to the strength of

Back 84

the chemical bonds between its atoms. The stronger the bond, the harder the crystal

Front 85

which takes a better polish when cut: A hard stone or a soft stone?

Back 85

A hard stone.

Front 86

most of the dust in the air is composed of _____ which has a hardness of __

Back 86

Quartz 7

Front 87

name the 5 levels of toughness

Back 87

exceptional excellent good fair poor

Front 88

Name 2 exceptional gems on the toughness scale

Back 88

jadeite and nephrite

Front 89

name an excellent gem on the toughness scale

Back 89

conrundum

Front 90

name 2 good gems on the tougness scale

Back 90

quartz and spinel

Front 91

name a fair gem on the toughness scale

Back 91

tourmaline

Front 92

name 2 poor gems on the toughness scale

Back 92

feldspar and topaz

Front 93

The different ways a gem breaks are called: 1. 2. 3.

Back 93

1. cleavage 2. parting 3. fracture

Front 94

define cleavage

Back 94

A smooth flat break in a gemstone parallel to planes of atomic weakness caused by weak or fewer bonds between atoms, or both.

Front 95

broken surfaces due to cleavage may have what kind of appearance

Back 95

step like

Front 96

How should gems subject to cleavage be mounted?

Back 96

mountings that protect a gem's corners and points provide the best protection.

Front 97

define parting

Back 97

a flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane

Front 98

define fracture

Back 98

any break in a gem other than cleavage or parting

Front 99

define conchoidal fracture

Back 99

a curved and ridged fracture in a gemstone, extending from the surface inward.

Front 100

define stability

Back 100

how well a gemstone resists light, heat and chemicals

Front 101

define thermal shock

Back 101

damage caused by sudden, extreme temperature changes

Front 102

A unit cell defines a mineral's

Back 102

basic identity

Front 103

If a crystal grows in a flux that is highly saturated with the necessary elements, it tends to be

Back 103

small

Front 104

which type of twinning is caused by environmental change after the gem forms

Back 104

polysynthetic