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GIA Graduate Gemologist - GEM 230 > Assignment 3 - How Diamonds Form > Flashcards

Assignment 3 - How Diamonds Form Flashcards

1
Q

What is a diamond made of?

A

Diamond (an graphite) are made of carbon.

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2
Q

What are the different layers within the earth

A
  • Crust
  • Mantle
  • Core
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3
Q

Why is plate tectonics important to diamond formation?

A

Subduction of plates is an essential part of diamond formation. Most diamond deposits are found on cratons or in the areas surrounding them.

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4
Q

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

A

Mineral

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5
Q

A natural material composed of one or more kinds of mineral

A

Rock

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6
Q

The surface and outermost layer of the earth.

A

Crust

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7
Q

The layer between the earth’s curst and core

A

Mantle

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8
Q

The earth’s innermost layer

A

Core

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9
Q

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

A

Lithosphere (100km)

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10
Q

The layer between the upper and lower mantles

A

Transition Zone
(410km to 660k)

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11
Q

The theory of the formation, structure and movement of earth’s landmasses.

A

Plate tectonics.

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12
Q

Any molten rock within the earth

A

Magma

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13
Q

Where in the earth’s structure are the best conditions for diamond formation?

A

Diamonds form under cratons, which are located only under continental land mass.

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14
Q

Ancient, large, and stable parts of the eartht’s continental crust

A

Cratons

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15
Q

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

A

Mantle keel

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16
Q

How do pressure and temperature make diamond the hardest substance on earth?

A

Pressure from 40 - 80 kBar.

Temperature from 900°C - 1’400°C

17
Q

The rate of temperature increase with depth in earth

A

Geothermal gradient

18
Q

What are the current models of diamond formation?

A

litospheric (in mantle keels below cratons)
superdeep (in transition zone and lower mantle)

19
Q

What types of rocks produce diamonds?

A

Periodite (Ignenous Rock) & Eclogite (Metamorphic Rock)

20
Q

Why do some diamonds (0.1%) have blue color?

A

Blue color mostly comes from boron trace, which originates from oceanic plates.

21
Q

A category of rocks from a molten state

A

Igneous Rock (Magmatisches Gestein)

22
Q

A category of rocks that have been altered by heat and pressure.

A

Metamorphic Rock (Metamorphes Gestein)

23
Q

A class of chemical compounds that contain carbon and oxygen

A

Carbonate

24
Q

Subduction

A

Process in which two crustal plates collide, forcing one under the other

25
Q

Which rocks deliver diamonds to the surface?

A

Kimberlite and lamproite transport diamonds to the surface, but diamonds are not formed in them.

26
Q

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

A

Crustal diamond

27
Q

An aggregate of many randomly oriented interlocking tiny diamond crystals that is the toughest form of diamond

A

Carbonado

28
Q

How do diamonds reach the surface?

A

Through emplacement of rocks from the cratons to the surface.

29
Q

When were diamonds delivered to the surface?

A

Diamonds exist today were delivered to the surface between 2.5bn and 20 million years ago.

30
Q

Kimberlite

A

An ingeous rock, that transports diamonds to the surface. It forms in the middle of the cratons.

31
Q

Lamproite

A

An ingeous rock, rarer than kimberlite, that transports diamonds to the surface.

32
Q

Emplacement

A

A geologic process that delivers materials to the surface.

33
Q

Pipe

A

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

34
Q

How does metasomatism affect lithospheric diamond formation?

A

It removes oxygen

35
Q

What layer of the earth includes continental and oceanic components?

A

Transition zone

36
Q

What is characteristic of superdeep CLIPPIR diamonds?

A
  • Cullinan-like
  • Large
  • Inclusion-poor
  • Pure
  • Irregular
  • Resorbed
37
Q

How many carats must bulk sampling produce for accurate evaluation of a primary deposit?

A

2’000 Carats

(in a sample of 5’000-10’000 tons)

38
Q

What are three most well-known examples for superdeep diamonds?

A
  • CLIPPR
  • Juìna (Brazil)
  • Blue Diamonds

GIA Graduate Gemologist - GEM 230 (20 decks)

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