A Charge-Coupled Device (CCD) collects both diffraction and fluorescence information. For example, when a sample containing the mineral halite (common table salt, or NaCl), was placed in CheMin, the instrument produced a specific diffraction pattern that identified that mineral’s structure.īecause all minerals diffract X-rays in a characteristic pattern and all elements emit X-rays with a unique set of energy levels, scientists can use the information from X-ray diffraction to identify the crystalline structure of materials the rover encounters on Mars. Scientists can measure the angle at which X-rays are diffracted toward the detector and use that to identify minerals. When this happens, they mutually reinforce each other and produce a distinctive signal. In X-ray diffraction, some X-rays bounce away at the same angle from the internal crystal structure in the sample. The analyzed material is finely ground, homogenized, and average bulk composition is determined. When the X-ray beam interacts with the rock or soil sample, some of the X-rays are absorbed by atoms in the sample and re-emitted or fluoresced at energies that are characteristic of the particular atoms present. What is X-ray Powder Diffraction (XRD) X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. They have a much shorter wavelength that cannot be seen with the naked eye. X-rays, like visible light, are a form of electromagnetic radiation. It uses a scoop for collecting soil.ĬheMin then directs a beam of X-rays as fine as a human hair through the powdered material. To prepare rock samples for analysis, the rover drills into rocks, collects the resulting fine powder, and delivers it to a sample holder. Scientists use CheMin to search for mineral clues indicative of a past Martian environment that might have supported life. Different minerals are linked to certain kinds of environments. Anhydrite is a calcium and sulfur mineral with no water in its crystal structure. For example, gypsum is a mineral that contains calcium, sulfur, and water. Using CheMin, scientists are able to study further the role that water, an essential ingredient for life as we know it, played in forming minerals on Mars. X-ray powder diffraction (XRPD) as a method of chemical analysis was first described in a paper by Hull (1919), in which he stated the following. Jarosite, found in sedimentary rocks by both the Curiosity and Opportunity rovers on Mars, precipitates out of water. For example, olivine and pyroxene, two primary minerals in basalt, form when lava solidifies. Minerals are indicative of environmental conditions that existed when they formed. Examples of minerals found on Mars so far are olivine, pyroxenes, hematite, magnetite, gypsum, and phyllosilicates. The Chemistry and Mineralogy instrument, or CheMin for short, identifies and measures the abundances of various minerals on Mars. A rotating wheel in the center of the rectangular housing will carry individual rock and soil samples for chemical analysis. Chemistry & Mineralogy X-Ray Diffraction Instrument: Designed to be about the size of a laptop computer inside a carrying case, the Chemistry and Mineralogy Instrument will identify and measure the abundances of minerals on Mars.
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