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Gemmology > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

What was limited before the 20th century despite diamonds being appreciated for centuries?

A

Scientific knowledge.

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2
Q

Why knowledge about about diamonds formation is important?

A

Knowledge makes easier prediction of locations of new diamonds sources.

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3
Q

What is key different property between diamond and graphite.

A

The type of bonding

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4
Q

What is earth’s basic structure.

A

The crust, mantle and core.

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5
Q

What is crust?

A

The surface and outermost layer of the earth, hard strong rock that’s extremly thin compared to the layers beneath it.

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6
Q

What is mantle?

A

The layer between the earth’s crust and its core.

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7
Q

What happened to the materials as the Earth solidified from clouds of gas and dust?

A

As the earth solidified from clouds of gas and dust, the denser materials were drawn toward the center and the lighter materials settled in the outer layers.

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8
Q

What is the thickness of crust?

A

Thickness ranges from about 5 to 40 km, though it can be much thicker under mountains ranges.

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9
Q

How many types of crust are there?

A

There are 2 types of crust: oceanic and continental.

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10
Q

Which crust is much thicker, insulating and generally made of lighter elements than other?

A

Continental.

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11
Q

What are the two types of crust, and where are they located?

A

Continental crust makes up the landmasses, and oceanic crust is present under oceans and seas.

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12
Q

What are the characteristics of oceanic crust?

A

Oceanic crust tends to be thin (5 to 7 km), cold, and comprised of much denser elements

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13
Q

What is diameter of earth?

A

6,300 km

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14
Q

What lies between the crust and the core, and what is its maximum thickness?

A

Between the crust and core is the mantle, which has a maximum thickness of about 2,880 km.

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15
Q

How mantle is divided?

A

The mantle can be divided into three broad layers: the upper mantle, lower mantle, and a transition zone in between.

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16
Q

At what depths does the division within the mantle occur?

A

Geologists divide mantle into upper and lower mantle, with the division occurring between 410 and 660 km.

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17
Q

What is the state of the mantle at its uppermost part, and how does it differ below this region?

A

The mantle is solid at its uppermost part. Below this it is also solid but mobile

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18
Q

What is the earth’s innermost layer?

A

Core

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19
Q

What is the lithosphere?

A

The layer that contains the crust and the uppermost part of the mantle.

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20
Q

What is transition zone?

A

The layer between the upper and lower mantles.

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21
Q

How one can divide mantle?

A

The mantle can be divided into three broad layers: the upper mantle, and a transition zone in between.

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22
Q

Till when there was no answer what was diamond as a susbtance?

A

Till late 1700’s.

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23
Q

When and who set a diamond in an oxygen filled glass jar and used a magnifying glass to direct a concentrated beam of sunlight on it?

A

French chemist Antoine-Laurent Lavoisier in 1772.

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24
Q

What Antoine-Laurent Lavoisier noted experiment showed?

A

He noted that the only byproduct of the burning diamond was carbon dioxide, the same thing happened with graphite.

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25
Q

Who and when converted identical weights of diamond and charcoal to exactly the same volume of carbon dioxide?

A

English chemist Smithson Tennant, he published his experiment in 1797.

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26
Q

How much time took for the scientific community to accept Tennant’s findings?

A

20 years

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27
Q

Definiton of mineral.

A

A natural inorganic substance with characteristic chemical composition and usually characteristic structure.

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28
Q

Definition of rock?

A

A natural material composed of one or more kinds of minerals

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29
Q

What is the difference between diamond and graphite?

A

Arrangement of carbon atoms

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30
Q

Why arrangement of carbon atoms in graphite and diamond are different?

A

Due to different environments, pressures, and temperatures during formation.

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31
Q

How many parts does the Earth’s core consist of?

A

Two. Outer and inner core.

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32
Q

What is the thickness of the Earth’s outer core, and what is its physical state?

A

The outer core is a molten (melted) layer about 2,270 km thick.

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33
Q

What is the physical state of the Earth’s inner core, and what is its approximate diameter?

A

Inner core is solid center about 2,400 km in diameter.

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34
Q

What is the approximate temperature of the Earth’s core, and how does it compare to the surface of the Sun?

A

Substantial heat radiates from the core, at about 6000 C, it’s as hot as some parts of the surface of the sun.

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35
Q

What prevents the Earth’s center from melting despite its high temperature, and how does the pressure at that depth compare to atmospheric pressure at sea level?

A

What keeps the center solid is the extreme pressure at that depth - in excess of 1 milion times greater pressure than the earth’s atmosphere at sea level.

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36
Q

How deep does the lithosphere extend beneath the Earth’s surface?

A

Lithosphere extends to appox. 100 km beneath the earth’s surface, but it can be thicker under mountain ranges and in diamond formation areas.

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37
Q

At what depth does the mobile upper mantle extend beneath the Earth’s surface, and how do its temperature and pressure compare to those of the lithosphere?

A

The mobile upper mantle, which extends from about 100 to 410 km beneath the earth’s surface, is under greater temperatures and pressures the the lithosphere.

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38
Q

What is the physical state of the crust and the uppermost part of the mantle?

A

It’s rigid.

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39
Q

What are the two sources of heat that make the solid mantle mobile, and what is their origin?

A

With two sources of heat - one from the core and one from the mantle, both derrived from the decay of radioactive elements - causes solid mantle to be mobile.

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40
Q

What drives the motion of the upper mantle and how does it influence the movement of lithospheric plates?

A

Motion of upper mantle is fueled by mantle convection - the warmer portions of the mantle rise and the colder portions sink - that drives the movement of lithospheric plates.

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41
Q

How is the mobile solid mantle divided, and what are the depth ranges for each part?

A

The mobile solid mantle can be divided into three parts: the upper mantle, from 100 to 410 km below the surface; the mantle transition zone, a boundary between the upper and lower mantles, from 410 to 660 km; and the lower mantle, from 660 to 2900 km.

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42
Q

What does the theory of plate tectonics explain about the Earth’s landmasses?

A

Plate tectonics explain the theory of the formation, structure, and movement of the earth’s landmasses

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43
Q

What drives the movement of the Earth’s plates?

A

Mantle’s convection drives the movement of the earth’s plate.

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44
Q

What is magma?

A

Any molten rock within the earth.

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45
Q

How is the lithosphere structured, and how many plates make up the Earth’s surface?

A

The lithosphere is broken up into what are known as plates. Fifteen plates, both continental and oceanic, make up surface of the earth.

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46
Q

For how long have the Earth’s plates been moving, according to estimates?

A

It is estimated that the plates have been moving for at least half of the planet’s history.

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47
Q

Do plate tectonics occur on other planets in the solar system?

A

Nope

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48
Q

What causes the movement of the mantle that forms convection currents, and how do sinking oceanic plates contribute to this process?

A

The heat generated from the radioactive decay of elements in the core and the lower part of the mantle causes hot mantle to rise and be cooled at shallower depths. Sinking oceanic plates push hot mantle from the transition zone upward. this movement of the mantle forms convection currents.

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49
Q

What is the term used to describe two tectonic plates that move away from each other?

A

Two plates that mover away from one another are called a spreading ridge.

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50
Q

What geological process occurs at mid-ocean ridges, and how does it contribute to the movement of tectonic plates and the increasing distance between continents?

A

Mid-ocean ridges are places where hotter convecting mantle rises and spreads to form new ocean floor. Sea floor spreading, part of plate tectonics, slowly pushes the plates apart, increasing the space between continents.

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51
Q

What is called Mid-Atlantic Ridge?

A

The ocean floor in the middle of the Atlantic Ocean is spreading as two tectonic plates move apart, which is visible on land where the rift runs through the center of Iceland.

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52
Q

What geological event occurs when two continental plates collide, and what is an example of this process?

A

When two continental plates collide, this creates a mountain-building event, such as when the Asian plate collided with the Indian plate and formed Himalayas.

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53
Q

What is growth rate of Himalayas nowadays?

A

An inch per year.

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54
Q

What is subduction?

A

The process in which a continental plate and an oceanic plate collide, forcing the oceanic plate down into the mantle.

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55
Q

What is cratons?

A

Large, ancient, stable parts of the earth’s landmasses.

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56
Q

What is essential part of diamond formation?

A

Subduction.

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57
Q

Where are most diamonds deposits found (geology)?

A

Diamonds are found on cratons or in the areas surrounding them.

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58
Q

What kind of elements are consisted in continental plates?

A

Continental plates consist of greater proportions of lighter elements such as oxygen, silicon, and aluminium.

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59
Q

What kind of elements are consisted in oceanic plates?

A

Oceanic plates are made up of greater proportions of heavier elements, such as iron, magnesium, and calcium.

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60
Q

What is mantle keel?

A

A large, downward protruding portion of the lithosphere under a craton.

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61
Q

What happens when a continental plate and an oceanic plate collide, and why does the oceanic plate sink beneath the continental plate?

A

When continental plate and an oceanic plate collide, the thinner colder, denser oceanic plate sinks under the continental plate.

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62
Q

What process occurs when one oceanic plate sinks beneath another, and what is this process called?

A

Subduction also occurs in the oceans simply by the sinking of one oceanic plate under another.

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63
Q

What type of crust and underlying material make up the oceanic plate?

A

The oceanic plate is made of a basaltic crust under which lies peridotite.

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64
Q

What transformation occurs to the basaltic composition of the oceanic crust as it is subducted under a continental plate, and what new rock type is formed?

A

The basaltic composition of the crust changes to another rock type - eclogite - as it descends into the mantle.

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65
Q

Why does the eclogite crust formed from the subduction of the oceanic plate contain a substantial amount of carbon?

A

Because the original oceanic plate contained a substantial amount of carbon.

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66
Q

What is an important source rock for diamond formation?

A

Eclogite.

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67
Q

Where subducted oceanic plate can descend?

A

It can descend far into the mantle, it may even reach the base of transition zone and upper part of of the lower mantle.

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68
Q

For how long have cratons not been active in plate tectonics?

A

Cratons have not been active in plate tectonics for millions and in some cases billions of years

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69
Q

Where are craton regions usually located, and what type of geological activity is not present?

A

Craton regions are usually in the middle of the continent and don’t experience earthquake activity.

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70
Q

Do the cratons exist under the oceans?

A

No

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71
Q

What cratons contain?

A

Cratons contain some of the oldest rocks on earth.

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72
Q

How old are rocks contained in cratons?

A

typically 2,5 billions years old up to 4 billion years at their center. /edges contain younger rocks/

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73
Q

How long diamond can stay within a mantle keel?

A

Million of years until an eruption carries it to surface.

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74
Q

Where do scientists believe the majority of diamonds are formed?

A

They believe that the majority of diamonds form in mantle keels.

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75
Q

How deep does the rigid lithosphere extend beneath cratons, starting from the base of the continental crust?

A

Beneath cratons the rigid lithosphere extends from the base of the continental crust, around 40 km to around 125 to 300 km.

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76
Q

What requires diamond formation?

A

Diamond formation requires right combination of extreme pressure, temperature and an environment with sufficient carbon.

77
Q

In what type of rocks do diamonds mainly form?

A

Eclogite and peridotite.

78
Q

What is the name of the rock formed from the molten state?

A

Igneous rock

79
Q

What is the name of rock that has been altered by heat and pressure?

A

Metamorphic rock

80
Q

What kind of minerals are contained in peridotite rock?

A

Mostly olivine, pyroxenes, garnet and spinel.

81
Q

What kind of rock is peridotite?

A

It’s igneous rock

82
Q

What kind of rock is eclogite?

A

It’s Metamorphic rock.

83
Q

What is peridotite?

A

It’s an ancient igneous rock that makes up the majority of the rigid lithosphere.

84
Q

Where does the carbon in peridotite come from?

A

It may have been inherited from the original carbon that formed with the earth come to existence.

85
Q

What is eclogite?

A

It’s a metamorphic rock that began as basaltic ocean crust.

86
Q

Where does the carbon in eclogite come from?

A

It can arise from organic matter in the ocean floor.

87
Q

What eclogite and peridotite have in common?

A

They contain carbon that can be source for diamond formation.

88
Q

What olivine, pyroxenes, garnet and spinel have in common?

A

They have a high content of magnesium, aluminum, and iron, but contain little to no silicon.

89
Q

What did scientists estimate about diamond formation after careful research?

A

Conditions for natural diamond formation are temperature range of 900 to 1400 C and pressure between 40 and 80 kilobars.

90
Q

What is normal pressure ate sea level?

A

1 bar

91
Q

What was the conclusion after geologists examined the types of rocks that carry diamonds to the surface?

A

They concluded that the right temperature and pressure exist in limited areas of the earth’s upper mantle, between 140 and 220 km.

92
Q

What are right conditions for forming and diamond?

A

900 to 1400 C, 40 to 80 kilobars. 140 to 220 km below the earth’s surface in the upper mantle.

93
Q

Do all diamonds form in mantle keels?

A

Nope, superdeep diamonds form much deeper in the mantle.

94
Q

When term “superdeep diamond” was established?

A

In the beginning of XXI century.

95
Q

Where superdeep diamonds form?

A

Superdeep diamonds form usually in transition zone 410-660 km and in the lower mantle (above 660 km).

96
Q

What is an indicator where a diamond formed within the earth?

A

Inclusion are good indicators.

97
Q

Where superdeep diamonds are found?

A

They are found in the same volcanic eruption deposits as lithospheric diamonds.

98
Q

Do all superdeep diamonds form in the same way?

A

No, superdeep diamond-forming fluids vary.

99
Q

What is common for superdeep diamonds formation?

A

Superdeep diamond formation is always related to, a subducted oceanic plate.

100
Q

What are three well studied examples of types of superdeep diamonds?

A

CLIPPIR, blue diamonds, Brazil’s Juna

101
Q

Does transition zone between mantles contain water?

A

Yes

102
Q

In which form transition zone contains water?

A

Not in fluid phase, but trapped as hydrogen bonded to oxygen in the crystal structures in high pressure-minerals such ringwoodite and wadsleyite.

103
Q

What kind of inclusions are found in superdeep diamonds?

A

ringwoodite, wadsleyite, bridgmanite, calcium peroskvite, and majoritic garnet.

104
Q

What is most common cause of blue color in diamonds?

A

Boron

105
Q

Where from originates boron in blue diamonds?

A

It originates from oceanic plates.

106
Q

Where from CLIPPIR diamonds crystallized?

A

CLIPPIR diamonds crystallized from metalic melts in the transition zone or the lower mantle.

107
Q

What process leads to the formation of diamonds in the Earth’s mantle, particularly in the transition zone?

A

Subduction of the oceanic crust down into the transition zone, where it starts to melt, releasing metallic melts containing carbon. The increased metalic content of the mantle at these depths creates a low-oxygen environment that allows diamonds to form.

108
Q

What CLIPPIR means?

A

Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed

109
Q

Why CLIPPIR diamonds have irregular shapes?

A

Because their surface is partially dissolved (resorbed).

110
Q

Why CLIPPIR diamonds are so important?

A

Because they are large and inclusion free.

111
Q

Name 3 CLIPPIR famous diamonds?

A

Cullinan 3,106 ct found in South Africa in 1905, Koh-i-Noor found in India in 1300’s, and the Lesedi la Rona 1,109 ct found in Botswana in 2015.

112
Q

Name largest square emerald cut diamond GIA has ever graded?

A

302,37 ct Graff Lesedi la Rona, D color, IF clarity

113
Q

Why metallic melts formed by subduction of the oceanic plate is ideal for CLIPPIR diamond formation?

A

Because this medium is an low-oxygen and rich in metals such as iron.

114
Q

Why iron is good for CLIPPIR diamond formation?

A

Iron can dissolve carbon from the oceanic plate without any oxygen.

115
Q

How much of mined diamonds are the blue diamonds?

A

0.1% are blue diamonds

116
Q

What you can say about inclusions in blue diamonds?

A

Inclusions in blue diamonds are rare and consist of mineral that do not exist in the upper mantle or transition zone.

117
Q

Does boron exist in lower mantle?

A

No

118
Q

Give an example of blue diamond found in 2014 in Cullinan mine?

A

The Blue Moon diamond. Rough was 29,62ct, polished 12,03 ct. (IF, Fancy Vivid Blue)

119
Q

What studies of inclusions in Juina diamonds indicated?

A

The these diamonds formed from carbonate fluids in the lower mantle.

120
Q

What is Carbonate?

A

Carbonate is a class of chemical compounds consisting of carbon and oxygen.

121
Q

What is principal component of rocks on the ocean floor and are a carbon source for diamond formation?

A

Carbonates

122
Q

How oxygen can be removed from the carbonate-rich fluids?

A

It can be removed at extreme depths under extremely high pressures and temperatures.

123
Q

What is crustal diamond?

A

Rare diamond that forms in the continental crust at or near the earth’s surface due to meteorite impact or tectonic plate collision.

124
Q

Where crustal diamonds form?

A

In the crust, near the earth’s surface.

125
Q

Are crustal diamonds common?

A

No, they are relatively rare.

126
Q

What is typical use of crustal diamonds?

A

Typically they’re used typically as abrasive.

127
Q

Name types of crustal diamond?

A

Impact diamond (meteorite strike to the earth’s carbon-rich surface). Diamond formed by ultrahigh pressure subjected on carbonate-rich rocks in tectonically active areas (plate collisions)

128
Q

Which diamond form is the toughest?

A

Carbonado.

129
Q

What is carbonado?

A

Carbonado is toughest form of diamond.

130
Q

Why carbonado is toughest form of diamond?

A

Because it’s an aggregate of many randomly oriented interlocking tiny diamond crystals that is the toughest form of diamond.

131
Q

Where carbonado is sourced?

A

In Brazil and the Central Republic of Africa.

132
Q

Describe carbonado?

A

It is usually opaque, dark in color, and porous, with a glassy appearance and an irregular surface.

133
Q

Is process of carbonado formation known?

A

It is still debated.

134
Q

How is called method of measuring age of material?

A

Method is called radiometric dating.

135
Q

When it’s possible to measure age of rock?

A

When one of the minerals in rock contain radioactive element.

136
Q

What happens with radioactive element as it decay?

A

As it emits atomic particles, it gradually changes into a different element.

137
Q

How scientists call change of radioactive element into a different one through a decay?

A

Daughter element.

138
Q

Is it possible to carbon date pure diamond?

A

No, it has to contain mineral inclusion that contain radioactive elements that can be extracted and used to infer the ages of the host.

139
Q

What are example of inclusions in diamond are useful in carbon dating?

A

Garnet and clinopyroxene.

140
Q

What is age of the oldest diamond studied?

A

Around billion years before the atmosphere became oxygenated and life arose on Earth 3,5 billion years ago.

141
Q

When diamonds were delivered to the surface of earth?

A

Diamonds were delivered to the surface between 2,5 billion and 20 million years ago.

142
Q

What are two igneous rocks that transport diamonds to the surface?

A

Kimberlite and lamproite.

143
Q

What is deepest hole ever drilled by human>

A

12 km deep

144
Q

What happens if diamonds spend too long under high temperatures and decreased pressures?

A

They will convert to graphite.

145
Q

What is eruption?

A

Eruption is a geological process that delivers material, sometimes diamonds, to the surface.

146
Q

Which kimberlite pipe is the largest one in Russia?

A

Mir pipe near Mirny in western Yakutia.

147
Q

Which is much more common diamond bearing igneous rock?

A

Kimberlite

148
Q

Do diamonds form in kimberlite or lamproite?

A

No, these rocks merely carry diamonds to the surface.

149
Q

What kind of rock is kimberlite?

A

It’s a silica-poor, magnesium-rich rock that contains mainly olivine. It is a mixture of melt, minerals, and rock fragments.

150
Q

What kind of rock is lamproite?

A

Lamproite is rich in potassium and magnesium; diamond bearing varieties contain olivine and lack feldspar.

151
Q

Which mine was the first deposit economically viable diamond-bearing lamproite discovered?

A

Argyle mine, Australia.

152
Q

For who Argyle source was important?

A

This source was important for the diamond industry as well for research.

153
Q

Where Kimberlites are tend to be found?

A

At the oldest parts of the continents.

154
Q

What is estimated travel speed of magma for the last 2,5 km before reach surface of lithosphere?

A

300 km/h

155
Q

What happens when gasses reach the lower pressures of shallower depths in the mantle?

A

Gasses expand and speed of kimberlite or lamproite magma’s rise.

156
Q

What kind of gasses are mostly contained in kimberlite and lamproite magma?

A

Water vapor and carbon dioxide.

157
Q

How kimberlite or lamproite magma transport diamonds to the surface?

A

On the explosive journey to the surface, kimberlite or lamproite magma encounter diamond host rock, the magma fractures it and transport the diamonds on it’s journey to the surface.

158
Q

How many diamonds and what color/clarity have being cut from the 1,109 ct Lesedi la Rona?

A

60 D color, Flawless/Internally Flawless diamonds.

159
Q

What forms pipe deposits?

A

Kimberlite and lamproite magma.

160
Q

What is definition of the pipe?

A

A deep vertical formation at the earth’s surface that results from a kimberlite or lamproite eruption.

161
Q

What means that diamonds are metastable?

A

It means they are stable only under the conditions in which they form.

162
Q

What is most important part of kimberlite or lamproite’s journey to the surface?

A

Speed, if it’s sufficient the environment changes and cools so quickly that the diamond’s carbon atoms don’t have time to alter their bonds and become graphite.

163
Q

Why kimberlite and lamproite solidify at quite high temperatures?

A

Because they have high melting points.

164
Q

What is the state of kimberlite and lamproite through the last few kilometers of the earth’s continental crust?

A

It is no longer molten state, it is a solid mixture of rock, ash, gases, and sometimes diamonds.

165
Q

What happens if kimberlite or lamproite stalls in earth’s crust?

A

Diamonds will convert to graphite.

166
Q

What is evidence of diamond conversion to graphite?

A

Diamond-shaped masses found in kimberlites.

167
Q

What kind of shape is produced by kimberlite blasts?

A

Deep carrot shaped formation.

168
Q

What kind of shape is produced by lamproite blasts?

A

Mushroom shaped formation.

169
Q

Which explosion is more violent kimberlite or lamproite?

A

Lamproite.

170
Q

Why lamproite and kimberlite produce differently shaped formation during eruptions?

A

Due to slight differences in chemistry and gas content.

171
Q

Are there many kimberlites or lamproites containing diamonds in economic quantities?

A

No

172
Q

How many kimberlites are known on continental cratons?

A

Around 6,000, but fewer than 1,000 contain diamonds.

173
Q

How many kimberlites have enough diamonds to be economic to mine?

A

About 50

174
Q

What have diamond and graphite in common?

A

They are both composed of carbon

175
Q

In which types of rock diamonds mainly form?

A

Peridotite and eclogite

176
Q

What is the origin of most mined diamonds?

A

Lithospheric and superdeep

177
Q

When diamonds form in mantle keels?

A

Diamonds form when carbon is available and free to bond with other carbon atoms without oxygen

178
Q

What is geothermal gradient?

A

The rate of temperature increase with depth in the earth.

179
Q

In what kind of lithosphere, temperature rises more rapidly with depth?

A

Oceanic lithosphere

180
Q

Why under the oceanic lithosphere there is no right conditions to form diamond?

A

There is no depth with right combination of temperature and pressure.

181
Q

Do diamonds form in the non-cratonic continental lithosphere?

A

No, because even in lower depths it is too thin to reach the necessary temperatures and pressures.

182
Q

Where are perfect conditions for diamonds to form and reside?

A

In cratonic lithosphere, mantle keels provide the perfect temperature and pressure.

183
Q

What is metasomatism?

A

A process in which chemical changes in mineral and rocks result from the introduction of material from external sources, often fluid or melts.

184
Q

In which conditions lithospheric diamonds form?

A

They form under crayons in mantle keels at around 140 to 220 km below earth’s surface, at temp. of 900 to 1400 C and pressure of 40 to 80 kilobars.

185
Q

What is carbon source for lithospheric diamonds

A

Mainly from peridotite, and sometimes eclogite.

186
Q

How is oxygen removed from eclogite and peridotite?

A

It’s done by fluids originating from deeper mantle, containing oxygen, carbon, hydrogen, and sulfur. Process is called metasomatism.

187
Q

What is superdeep diamonds?

A

Diamonds that formed at 410 km or deeper beneath the earth surface.

188
Q
A

Gemmology (11 decks)

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