garnets
The abrasive grain, the key part of coated abrasive products, may be either a natural or synthetic mineral. Due to their extreme hardness, natural minerals such as http://www.answers.com/topic/garnet, quartz or http://www.answers.com/topic/emery (corundum with iron impurities) have uses in sandpaper and grinding tools.
This mineral is hydroxyapatite.
Your sandpaper is graded according to the amount of abrasive particles (grit) per square inch. The six abrasive categories range from course to super fine and between them include medium, fine, very fine and extra fine. Your choices will depend on the finish you hope to achieve. These particles or categories consist of one of four minerals that make up sandpaper: aluminum oxide, garnet, ceramic (alumina zirconia) and silicon carbide. Read more: What Mineral Is Used in Sandpaper? | Garden Guides http://www.gardenguides.com/135206-mineral-used-sandpaper.html#ixzz1ndZpWlRk
Calcium
Sandpaper is made with corundum because it is extremely hard (9 on the Moh's Scale of Hardness) compared to just about anything else, except diamond (which top the scale at 10). This "hardness" is basically the factor which determines what happens when scraped against another material. If the corundum in the sandpaper is harder than whatever you are rubbing it against, then it will scratch the surface. If the sandpaper is used on something harder than corundum, the sandpaper will not be able to leave abrasions. Corundum is used because there are very few materials which it will fail to scratch.
They were made from flint. Flint is a hard, sedimentary form of the mineral quartz.
To put sandpaper on a sander, first make sure the sander is turned off and unplugged. Then, align the sandpaper with the sander's base and secure it using the clips or adhesive on the sander. Make sure the sandpaper is taut and smooth before turning on the sander to use.
One can make water hard by adding minerals such as calcium and magnesium to it. These minerals can increase the water's mineral content, making it harder.
Saltwater is considered hard because it contains dissolved minerals, such as calcium and magnesium, which increase its overall mineral content. This higher mineral content can make the water less effective at lathering soap and can contribute to mineral buildup in pipes and appliances.
Mineral salts from calcium and phosphorus compounds are essential for making bones hard and strong. calcium is the most essential mineral to make bones strong but not all bones are as hard as you think some bones are "Spongy" but we just dont notice it. hope this helps if you need to know this....
because it makes the skin moist making it easier to use as sandpaper:)
Copper
You use cardboard and diamond dust.