. Bulletin - New York State Museum. Science. GUIDK TO THE MIXEKALOGIC COLLECTIONS 41 mamillary, like the botryoidal but composed of larger and flatter protuberances, example malachite, pi. 62 globular, imperfect spheres of radiating fibers, examples wavellite, pectolite, pi. 7X oolitic, composed of small rounded grains, like the roe of fish, example calcite, pi. 72 coralloidal, consisting of branching forms like coral, exam- ple aragonite, pi. 8X dendritic, in branching treelike forms, example pyrolusite, pi. So stalactitic, in pendant columns from the roofs of caves, formed by percolation of
. Bulletin - New York State Museum. Science. GUIDK TO THE MIXEKALOGIC COLLECTIONS 41 mamillary, like the botryoidal but composed of larger and flatter protuberances, example malachite, pi. 62 globular, imperfect spheres of radiating fibers, examples wavellite, pectolite, pi. 7X oolitic, composed of small rounded grains, like the roe of fish, example calcite, pi. 72 coralloidal, consisting of branching forms like coral, exam- ple aragonite, pi. 8X dendritic, in branching treelike forms, example pyrolusite, pi. So stalactitic, in pendant columns from the roofs of caves, formed by percolation of water carrying dissolved mate- rial, example calcite, limonite, pi. 9X acicular, slender, needlelike forms, example stibnite, pi. 92 capillary, hairlike, example millerite, pi. lO^ reticulated, interlaced fibers like a net, example stibnite, pi. 102. Cleavage Closely related to the crystalline structure of a mineral is the tendency, common in a varying degree to most mineral species, to break or split parallel to cer- tain crystallographic planes. This ten- dency, which is called cleavage,takes place along the lines of minimum cohesion. Thus in a cube, the molecular arrangement of which is shown in fig. 2, it would be reasonable to expect cleavage to take place along planes parallel to the cube faces, that is,along the planes of molecular crowd- ing. In fig. 156, assuming the dots to represent the position of molecules, the lines of least resistance to cohesion and con- sequently the lines of cleavage would be the vertical and hori- zontal rather than either of the inclined lines because the par- allel lines of molecules on either side of the vertical and hori- zontal directions are further apart and consequently the attract- ive force betweeE adjacent molecules would lie least along flics'- lines. In isometric minerals cleavage takes place parallel l<» the. Fig. 156. Please note that these images are extracted from scanned page images that may have been digitally enhanced
Size: 1571px × 1590px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectscience, bookyear1887
