[f. CLEAVE v. + -AGE.]
1. The action of cleaving or splitting crystals and certain rocks along their lines of natural fissure; the state of being so cleft.
1816. P. Cleaveland, Min., 9. The primitive forms of crystals can be ascertained only by mechanical division. This process, sometimes called cleavage by lapidaries, consists in separating thin layers or slices from the sides, edges, or angles of a crystallized substance in a given direction.
1831. Brewster, Optics, xvii. § 90. 145. We may by a new cleavage replace the imperfect face by a better one.
b. Min. Arrangement in laminæ which can be split asunder, and along the planes of which the substance naturally splits; fissile structure; the property of splitting along such planes.
1830. Sir J. Herschel, Stud. Nat. Phil., 291. The texture or cleavage of a mineral.
1869. Roscoe, Elem. Chem., 191. Crystalline bodies exhibit … a peculiar power of splitting in certain directions more readily than in others, called cleavage.
c. Geol. Slaty cleavage: the fissile structure in certain rocks, especially in clay slate and similar argillaceous rocks, whereby these split into the thin laminæ or ‘slates’ used in roofing, etc. This structure is quite distinct from, and in origin posterior to the stratification and jointing, the cleavage-lines crossing these at any and every angle, while parallel to themselves over extensive tracts of country.
1839. Murchison, Silurian Syst., 574. The observation of Professor Sedgwick on the slaty cleavage of mountains.
1839. Darwin, Voy. Nat., vi. 135. A formation of quartz which … had neither cleavage or stratification.
1860. Tyndall, Glac., I. § 1. 2. I learned that cleavage and stratification were things totally distinct from each other.
1882. Geikie, Text-bk. Geol., II. II. § 6. 121. This superinduced fissility or ‘cleavage’ has resulted from an internal rearrangement of the particles in planes perpendicular to the direction in which the rocks have been compressed.
d. (with pl.) The direction or plane in which a crystal or rock may be split.
1817. R. Jameson, Char. Min., 135. The cleavages are not parallel with any of the planes of the crystal.
1869. Tyndall, Light, 73. By following these three cleavages it is easy to obtain from the crystal diamond-shaped laminæ of any required thinness.
2. gen. The action or faculty of cleaving or splitting asunder; the state of being cleft; division. lit. and fig.
1867. Froude, Short Stud., Erasm. & Luther (ed. 2), 26. When differences of religious opinion arose, they split society to its foundation. The lines of cleavage penetrated everywhere.
1879. Baring-Gould, Germany, I. 60. We lament, in England, the cleavage between the classes, but it is nothing to that which exists in Germany.
1886. Spurgeon, Treas. Dav., Ps. cxliii. Introd. This psalm is divided by the Selah. We prefer to follow the natural cleavage, and therefore have made no other dissection of it.
3. attrib., esp. in cleavage-plane.
1831. Brewster, Optics, xxv. 214. Analcime has certainly no cleavage planes.
1862. Dana, Man. Geol., 55. A broad, even, lustrous cleavage-surface.
1875. J. W. Dawson, Dawn of Life, v. 117. The loganite … shows traces of cleavage-lines.
1878. Gurney, Crystallog., 8. Most crystals can be separated into indefinitely thin slices, which are bounded by flat surfaces called cleavage-planes.
1882. Geikie, Text-bk. Geol., II. II. § 6. 121. ‘Clay-slate’ has generally been applied solely to argillaceous rocks possessing this cleavage-structure.
