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Xenolith
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Rock fragment foreign to igneous rock in which it occurs. Commonly inclusion of country rock intruded by igneous rock
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Xanthoconite
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A monoclinic mineral, Ag3 AsS3 ; dimorphous with proustite; brilliant red, orange-yellow to brown. Syn: rittingerite
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Xenotime
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A tetragonal mineral, YPO4 ; commonly includes small quantities of thorium, uranium, and rare-earth elements; resembles zircon in form, structure, and occurrence; shows pale tints; an accessory in granites and pegmatites; also occurs in placers.
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Xyloretinite
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A white hydrocarbon similar to hartite found in fossil wood.
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X-axis
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A. The axis of abscissas in a plane Cartesian coordinate system. Commonly written x-axis.
B. One of the three optic axes (x, y, and z) in a biaxial crystal. The x-axis is the axis of a greatest ease of vibration. Light vibrating parallel to the x-axis travels with maximum velocity and is called the fast ray, the x-ray (not to be confused with the penetrating X-rays of extremely short wavelength), and the alpha -ray. The lowest index of refraction nalpha . in biaxial minerals is the index of the fast ray vibrating parallel to the x-axis.
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X-axis
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A. The axis of abscissas in a plane Cartesian coordinate system. Commonly written x-axis.
B. One of the three optic axes (x, y, and z) in a biaxial crystal. The x-axis is the axis of a greatest ease of vibration. Light vibrating parallel to the x-axis travels with maximum velocity and is called the fast ray, the x-ray (not to be confused with the penetrating X-rays of extremely short wavelength), and the alpha -ray. The lowest index of refraction nalpha . in biaxial minerals is the index of the fast ray vibrating parallel to the x-axis.
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Xenoblastic
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Applied to a texture of metamorphic rocks in which the constituent mineral grains lack proper crystal faces.
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Xanthitane
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An alteration product of titanite (sphene).
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Xanthophyllite
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. A monoclinic mineral, Ca(Mg,Al)3 (Al3 Si)O10 (OH)
2 ; mica group. Syn:seyberite
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Xonotlite
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A monoclinic and triclinic mineral, Ca6 Si6 O17 (OH) 2 ; light-gray to pink; fibrous; in serpentinites in Santa Barbara, CA, and on Isle Royale, MI.
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