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Geological Terms Beginning With "X"

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A crystal that has grown in a rock during the process of metamorphism and which has not developed its characteristic crystal faces because of space limitations. These crystals typically have boundaries that are straight or that conform to the shape of adjacent crystals. The photo shows quartz and feldspar grains in a gneiss.



A preexisting rock that has been incorporated into magma without melting. When the magma crystallizes the preexisting rock fragment is known as a xenolith.



A plant that can survive in a very dry location or climate because it has a well-developed means of storing and conserving water. The image shows a group of cacti living on a desert floor.

X-ray Diffraction

X-ray Diffraction (XRD)

A technique used to identify minerals and other crystalline materials by bombarding them with X-rays. Planes of repetition within the atomic structure of the mineral diffract the X-rays. The pattern of diffraction is unique for each mineral structure and can be used for identification. This method of identification is much more reliable than hand-specimen identification and is used when hand-specimen identification is not possible or difficult.

X-ray Diffractogram

X-ray Diffractogram

A printed or digital record of an x-ray diffraction analysis. It shows the angle of diffraction on the horizontal axis and the intensity of diffraction on the vertical axis. Peaks on the diffractogram are characteristic of the material being examined and can be compared with reference diffractograms to identify minerals and other crystalline compounds.

X-ray fluorescence

X-ray Fluorescence (XRF)

A technique used to determine the elemental composition of a specimen by bombarding the material with x-rays. The x-rays excite the atoms in the specimen causing them to emit x-rays of a longer wavelength. These are detected by the analytical equipment and on the basis of comparison with known standards the elemental composition of the specimen is determined.

xyloid coal

Xyloid Coal

A type of lignite coal that displays the fibrous structure of the wood. Also known as "xyloid lignite".

Dictionary of Geological Terms   Dictionary of Geological Terms

All scientific disciplines have an essential vocabulary that students and professionals must understand to learn and communicate effectively. A geology dictionary that is used reguarly is one of the most important tools for developing professional competence. A good dictionary should be on the desk of every geologist and within easy reach. This dictionary is compact and inexpensive at only $18.95. More information.
xyloid coal


An opalized wood. Forms when common opal infills the cavities and replaces the organic material of a piece of wood. Sometimes the wood grain or cellular details of the original wood can be seen..

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