| Hardness is an important factor in resistance to erosion. The hardness of geologic materials, such as rocks and sediment, depends on the hardness of the individual mineral grains out of which they are made. The table on the right gives approximate Mohs values of all but three of the minerals that are the most important components of the NYC materials. You will determine the hardnesses of garnet, labradorite and magnetite using the NYC Minerals Hardness Testing Lab.
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