426 



Calcareous Containing a large proportion of carbonate of lime. 



Cancellated Latticed ; crossed by two series of parallel lines, as some triclinic 

 felspars when twinned simultaneously on the albite and pericline types. 



Carbonaceous Containing some form of carbon, such as graphite or coal. 



CataelastiC A general term used by Kjerulf (Nyt. Mag. XXIX. 3, 269) to 

 embrace all structures produced in rocks by a crushing of the constituent 

 minerals. The separation of the broken mineral fragments can often be 

 clearly made out under the microscope. See Clastic. 



CatOgeniC A term used in geology, in contradistinction to anoyenic, to designate 

 rocks which have been deposited. It is thus synonymous with aqueous. 



Cellular Containing irregular spheroidal or ellipsoidal cavities, as many lavas. 

 The cellular structure is produced by the expansion of steam in the molten 

 rock. See Vesicular, Pumiceous, Scoriaceous. 



Centric Structure The name given to certain stellate arrangements of 

 crystals, grains, or microlites around a central grain or aggregate of 

 grains. This structure is common to both eruptive rocks and the banded 

 crystalline series. Syn. Ocellar structure. 



Chatoyant Exhibiting a changeable lustre like that of the cat's-eye (ceil-de- 

 chat). Chatoyancy is allied to opalescence ; according to Prof. Judd, it is 

 caused by the presence of ultra-microscopic particles. 



Cherty Composed of, or resembling, chert. 

 Chloritic Containing one of the chlorite minerals. 



Clastic Composed of fragmentary material, as the conglomerates, breccias, and 

 sandstones. Mr. Teall (" Origin of Banded Gneisses," Geol. Mag., Nov., 

 1887, p. 493) suggests that this term should be applied to all rocks 

 which consist largely of mineral fragments, and that we should distinguish 

 between the three types of clastic rocks at present recognized, by using 

 the terms epiclastic, cataclastic, and pyroclastic. Epiclastic Kocks formed 

 of fragments resulting from the breaking up of older rocks upon the earth's 

 surface. Cataclastic Eocks largely composed of fragments produced 

 during the deformation of older rocks by the earth-stresses. Pyroclastic 

 Fragmental rocks of volcanic origin." 



Clavate Club-shaped. 



Cleavage (1) As applied to minerals. ((jrer. Spaltbarkeit.) The property 

 possessed by minerals of separating along certain planes. These cleavage- 

 planes are parallel to the faces of one or more of the crystalline forms 

 of the mineral. 



(2) As applied to rocks. (Ger. Schieferung.) The fissile structure 

 characterizing slates is also termed cleavage. These rocks split 

 easily into thin laminae along planes which do not necessarily coincide 

 with, and bear no genetic relation to, those of bedding. Sorby 

 and Tyndall have shown that cleavage can be produced artificially 

 in a rock by pressure, the planes of cleavage being perpendicular to the 

 direction thereof ; and to this cause the phenomena of cleavage are now 

 generally referred. 



Cleavage-foliation A term applied to that kind of foliation which is due to 

 the development of secondary minerals along planes of cleavage. 



Clinodiagpnal The name sometimes given to the inclined axis in the mono- 

 clinic system of crystals. 



Clinopinacoid One of the three principal crystallographic planes in the 

 monoclinic system. It coincides with the plane of symmetry, and runs 

 parallel to the vertical and to the inclined axis. 



