The primary function of the CheMin will be to study mineral composition formed by the action of liquid water and how other mineral substances were formed in the absence of water. Some of the minerals already found on previous Mars missions include magnetite, gypsum goethite, pyroxenes, olivine, jarosite and hematite. The CheMin will be looking for many other minerals and how they may have been formed by the movement of water. The MER rover Opportunity discovered erosion in solid rock in the walls of Endurance Crater, believed to be the result of flowing water. The MSL will collect small stones or pebbles and deposit them in a rock crusher which will grind them to almost a powder. A sieve will ensure that the smallest grains are placed on a sample holder, which will vibrate to mix the sample. CheMin will then pass X-rays through the sample to produce X-ray diffraction which will be absorbed by a detector. This will identify the specific minerals in the sample because each mineral has a distinct diffraction pattern. A charge-coupled device (CCD) will collect diffraction and fluorescence given off during the X-ray operation.
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