camera axis . A line perpendicular to the focal plane of the camera and passing through the interior perspective center or emergent (rear) nodal point of the lens system.

alamosite (al-a-mos'-ite). A colorless, white, cream or light gray monoclinic mineral: PbSiO₃ . It has a 12-repeat pyroxene-like chain.

crystal-structure solution . The determination of the approximate fractional coordinates for the atoms of a crystal structure by any of several methods, usually involving diffraction data. Syn: structure solution.

volcanic rock . (a) A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the Earth's surface, either ejected explosively or extruded as lava; e.g. basalt. The term includes near-surface intrusions that form a part of the volcanic structure. See also: volcanics. Cf: plutonic rock. (b) A general term proposed by Read (1944) to include the effusive rocks and associated high-level intrusive rocks; they are dominantly basic. Cf: neptunic rock; plutonic rock.

mesonorm (mes'-o-norm). Theoretical calculation of normative minerals in metamorphic rocks of the mesozone from chemical analyses (Barth, 1959). Cf: catanorm; epinorm. See also: Niggli molecular norm.

ecocline (ec'-o-cline). A cline related to the gradation between two different niches.

structural crystallography . Study of the internal arrangement and spacing of atoms and molecules composing crystalline solids.

alkali-feldspar syenite . In the IUGS classification, a plutonic rock with Q between 0 and 5, and P/(A+P) less than 10.

foot [geol] . (a) The bottom of a slope, grade, or declivity. Cf: head [geomorph]. (b) That portion of the displaced material of a landslide that lies downslope from the toe of the surface of rupture (Varnes, 1978). (c) The lower bend of a fold or structural terrace. Syn: lower break.

hause . An English term for a pass, or a ridge connecting two higher elevations, or a narrow gorge (Whitney, 1888, p.137). Cf: hals. Syn: haws.