Diamonds of North America
by Patrick Laird


Image taken from Diamonds.com


Introduction
Formation
Location
Diamond Deposits
Exploration
Mining
North America Mines
References




Introduction

Image taken from
Diamonds on web.

When diamonds are mentioned, most of us think of South Africa.  While most of the gemstone grade diamonds do come from South Africa, diamonds are found everywhere but in Europe.  One of the most surprising areas to find diamonds are in the United States and Canada.  Although the majority of these diamonds are used for industrial purposes, the occasional rare or large gemstone grade diamond has been known to surface.  Throughout this web site are different areas dealing with diamonds of North America, from occurrence to mines.  This web site was created to fulfill the requirements of GO340 Gemstones & Gemology being offered through Emporia State University during the spring semester of 2002.

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How Diamonds Form
Diamond is made up of carbon, as is graphite.  The carbon atoms of diamond are packed much closer together than graphite and take on the shape of a cube, referring to the isometric system.  They are formed at great depths, more than 150 kilometers, over a long period of time well below the Earth's surface as a result of  pressure.  Since diamond form under great pressure, they are rarely formed on or near the surface of the Earth.  As diamond is formed deep below the surface under great pressure, it makes it extremely hard and durable as it comes to the surface.  It is less likely to weather than any other mineral and is used for industrial purposes and as well as gemstones for jewelry. (Diamonds - American Museum of Natural History)


A picture of a diamond in the rough.
Image taken from Canada Institute
of Gemology.

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Where Diamonds Are Found
Diamonds are found on continents and are associated with past volcanic activity.  Cratons, which are the oldest parts of a continent, are especially favorable for hosting diamonds because they are older than the newer crust.  As the older crust contained volcanoes, kimberlite and lamproite magmas transported the diamonds to the surface.  When these old volcanic magmas called kimberlite pipes are uncovered, they are susceptible to weathering, leaving the diamonds exposed on the surface of the Earth. (Diamonds - American Museum of Natural History)
 
 


Cross section of a kimberlite pipe. Image taken from
Canadian Rockhound.

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Types of Diamond Deposits
There are two types of diamond deposits, a primary deposit and a secondary deposit.  Primary deposits are the kimberlite pipes that bring the diamonds to the surface.  In North America, these pipes are were diamonds are mined.  A secondary deposit is caused by erosion, which transports the diamond to another place.  The most common secondary deposit is also associated with a kimberlite pipe.  This is due to weathering of the kimberlite rock exposing the diamonds.  Much of these diamonds are still found near the original kimberlite pipe.  Gravity and water also play an important part in secondary deposits.  If the pipe is elevated above the surrounding landscape, diamonds can be washed to a lower area by rain water.  If the water washes them into the a creek or river, the diamonds can be transported even further from the pipe.  As diamonds have a high specific gravity of 3.5, they are usually deposited in slow moving water as the rest of the material will continue to travel downstream. (Diamonds - American Museum of Natural History)


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