Key Concepts

Diamond

A form of carbon that is typically transparent and has a crystal structure.

Graphite

Another form of carbon that is opaque and consists of layers of carbon atoms.

Earth's basic structure

Consists of the crust, mantle, and core.

Mantle layers

Composed of the upper mantle, lower mantle, and a transition zone in between.

Mantle convection

The process that drives the movement of the earth's plates.

Subduction

An essential part of diamond formation.

Cratons

Stable portions of the continental crust where most diamond deposits are found.

Types of rocks diamonds form in

Primarily in peridotite and eclogite.

Conditions for diamond formation

Require extreme pressures and temperatures, along with a source of carbon.

Mantle keel

The region within the mantle where the conditions for diamond formation exist.

Lithospheric diamonds

Diamonds that are mined and originate from within the lithosphere.

Superdeep diamonds

Diamonds that form much deeper within the mantle as compared to others.

Carbon source for diamond formation

Needs to be available and free to bond with other carbon atoms without oxygen.

Inclusions in diamonds

Can indicate where a diamond formed within the earth.

CLIPPIR diamonds

Diamonds that crystallized from metallic melts in the transition zone or lower mantle.

Blue color in diamonds

Commonly caused by the presence of boron.

Boron origin in blue diamonds

Comes from oceanic plates.

Carbonado

The toughest form of diamond.

Timeframe for diamonds reaching surface

Delivered to the surface between 2.5 billion and 20 million years ago.

Rock types that transport diamonds

Kimberlite and lamproite.

Frequency of kimberlite versus lamproite

Diamond-bearing kimberlite is much more common than diamond-bearing lamproite.

Location of kimberlite

Tends to occur in the center of cratons.

Location of lamproite

Occurs at the edges of cratons.

Deposit type for kimberlite and lamproite

Form pipe deposits.

Occurrence of diamonds in kimberlite or lamproite

Very few contain diamonds in economic quantities.