1. Abrasives ©2009 Dr B C Paul Acknowledgement is given to the following sources SME Industrial Minerals, mcrocks.com, geology.com, webmineral.com, mindat.org, USGS, cs.cmu.edu, yuprocks.com, gc.maricopa.edu

2. Good Abrasives They are cheap They last a long time They cut or wear surfaces that you want cut or worn quickly They don’t cut things you don’t want them to Hardness is an obvious important factor Size and shape also are important

3. Diamonds Hardness of the diamond is unmatched and for many applications they are irreplaceable for cutting –Industrial diamonds lack the color and perfection of jewlery Major uses –Diamond bits for rock and concrete –Diamond dies for wire drawing –Diamond tipped tools and wheels

4. (from Rockhoundblog.com)

5. Diamond Locations Diamonds are typically found in Kimberlite and Lamproite intrusions The intrusions can be as recent as the Cenozoic –Diamonds themselves are usually older Most are 3,200,000,000 to 990,000,000 years old A few have been found back to 4,200,000,000 All seem to be associated with Archean basement (maybe a few younger)

6. Roots of Continents Deeper than Crust At these depths stable form of carbon switches from graphite to Diamond

7. Melts Coming Up from Depth Drag Diamonds to the Surface Kimberlite does not make diamonds It drags them

8. Where is Archean Crust Known to be Found Red and Dark Green Mark the Spot

9. The Missing Crust Problem Stabilization of the Mantle Composition relative to earth’s crust appears to happen around 2,700,000,000 years ago –We should have 70 to 80% of the continental crust by then

10. Closer View of North American Old Crust Areas

11. Industrial Diamonds C S.G. 3.5 - 3.53 Hardness 10 Color Colourless, yellowish to yellow, brown, black, blue, green or red, pink, champagne-tan, cognac-brown, lilac (very rare)

12. How Diamonds are Processed Crushing and Grinding –(if the deposit is weathered or a placer this may not be needed) Gravity Concentration –Diamonds are heavier than surrounding minerals –some unique designs produce a concentrate of heavy minerals Rotary washing pan Make mud and the Heavies settle

13. Heavy Media This diagram shows how cones (left) and cyclones (right) use heavy-media separation. Diamond-bearing concentrate is mixed with a fluid near the density of diamond. Separation occurs in cones and cyclones by swirling the mixture at low and high velocities respectively. In the cone, rotational mixing permits lighter minerals to float to the top and run out as overflow, while diamonds and dense minerals sink to the bottom and are sucked out with a compressed air siphon. In the cyclone, fast rotation of the suspension drives heavy minerals to the conical wall, where they sink to the bottom and are extracted, while float waste minerals are sucked from the center of the vortex. Cyclones are about 99.999% efficient at concentrating diamonds and similarly dense minerals from the original ore. Adapted from Bruton (1978)

14. Other Minerals Besides Diamonds are Heavy The grease method –Freshly exposed diamonds grab onto axle grease –Use greased shaking tables to pull out diamond

15. An Alternative to Hand Sorting of Concentrates Using Fluorescence

16. Reserves and Production Catch – 88% of industrial diamonds are now synthetic

17. What are Diamonds Worth Ability to make synthetic diamonds has brought down the price but they are Still over $1,000,000 per ton (of course they are sold by carrots)

18. Corundum/ Emery Lots of gems are corundum Much of abrasive market has been taken by synthetic minerals –Get more uniform material without random natural weaknesses –Still used for super heavy duty concrete and durable anti-skid material

19. Corundum Al 2 O 3 S.G. 3.98 - 4.1 Hardness 9 Color Colourless, blue, red, pink, yellow, grey, golden-brown Gem forms include Rubies and Sapphires, Emery

20. Where Corundum is Found

21. Garnet Use as a grinding and polishing agent –Garnet papers still common abrasive –Also used as a “sand blasting agent” It does not cause silicosis –Filtering material –A lot of natural sharpening rocks in fact get their properties from well distributed small garnet crystals

22. Almandite Fe 3 Al 2 (SiO 4 ) 3 S.G. 4.09 - 4.31, Average = 4.19 Hardness 7-8 Color Brown, Brownish red, Red, Black, Black red. Fluorescence None

23. Grossularite Ca 3 Al 2 (SiO 4 ) 3 S.G. 3.42 - 3.72, Average = 3.57 Hardness 6.5-7.5 Color Brown, Colorless, Green, Gray, Yellow. Fluorescence None

24. Pyrope Mg 3 Al 2 [SiO 4 ] 3 S.G. 3.5 - 3.6 Hardness 7.5 Color Blood red, orange red, purple red, pink, or black red Fluorescence not reported

25. Andradite Ca 3 Fe 2 (SiO 4 ) 3 S.G. 3.8 - 3.9 Hardness 6½ - 7½ Color Green, yellow, orange, reddish-brown, brown, black Fluorescence not reported

26. Staurolite Industrial application is as a “Sand Blasting Agent” Also used as a gemstone

27. Staurolite (Fe,Mg) 2 Al 9 (Si,Al) 4 O 20 (O,OH) 4 S.G. 3.65 - 3.77, Average = 3.71 Hardness 7-7.5 Color Brownish yellow, Brownish black, Yellow brown, Dark brown, Reddish brown. Fluorescence not reported

28. Silica Sand is still dominant material for “Sand Blasting” Carefully graded and sized sand is used for “flint” sandpapers –Dominant market is home use Fine pure sands are an important raw material for glass, ceramics, and synthetic abrasives Naturally fine almost amorphous material that breaks up easily is called Tripoli

29. Sand SiO 2 S.G. 2.6 - 2.65, Average = 2.62 Hardness 7 Color Brown, Colorless, Violet, Gray, Yellow. Fluorescence not reported

30. Tripoli SiO2 S.G. 2.7 Hardness 7 Color White, buff Fluorescence None Magnetic- No

31. Soft Scrubbing Powders Diatomite –Used in silver polishes –More common use is filtering media Pumice –Main ingrediant in polishing powders and household cleaners Including tooth paste –Used in hard rubbers –Used for washing stones for blue jeans

32. Pumice Pumice is about 60-70% silica It has no crystal structure – it is a frothy glass S.G. < 1

33. Other Soft Abrasives Ground Feldspar in window cleaners Chalk for fine soft metal polishes Kaolin

34. Synthetic Abrasives Silicon Carbide and related (Tungsten Carbide)