132 NEW YORK STATE MUSEUM 



APPENDIX 



GLOSSARY OF CR YSTALLOGR APH1 C TERMS 

 Acicular. Needlelike in structure. 



Arborescent. With a branching structure like a tree or plant. 



Axes. Imaginary lines drawn within a crystal for the purpose of study- 

 ing the relation of its planes. 



Axial ratio. The relations between the lengths of axes which are not 

 interchangeable as determined by the intercepts of a prominent pyramid 

 face. 



Basal plane or base. A plane which truncates the crystal parallel to the 

 basal axes. 



Biaxial crystals. A term used to include in an optical division crystals 



of the orthorhombic, monoclinic and triclinic systems. 

 Binary. Twofold. 



Bladed structure. Composed of bundles of broad flat crystals resembling 



the blades of knives. 

 Botryoidal. Derived from a Greek word meaning a bunch of grapes. 

 Brachyaxis. The shorter of the two basal axes in the orthorhombic and 



triclinic systems. The term brachy is derived from a Greek word 



meaning short. 



Brachydomes. Domes or horizontal prisms parallel to the brachyaxis. 

 Brachypinacoid. A pinacoidal plane parallel to the vertical and brachy 

 axes. 



Brachyprisms, brachypyramids. Crystal forms the planes of which are 

 more nearly parallel to the brachyaxis then those of the form which 

 determines the axial ratio. [See p. 32, fig. 124] 



Capillary crystals. Extremely elongated individuals resembling hairs or 

 threads. 



Clinoaxis. The axis which in the monoclinic system is oblique to the 

 plane of the other two but is perpendicular to one of the latter. 



Clinodomes. Domes or horizontal prisms the faces of which are parallel 

 to the clinoaxis. 



Clinopinacoid. A pinacoid parallel to the vertical and clino axes. 



Clinoprisms, clinopyramids. Crystal forms the faces of which are more 

 parallel to the clinoaxis than the form which determines the axial ratio. 



Columnar structure. Composed of aggregates of elongated crystals re- 

 sembling columns. 



Coralloidal. Branching and interlacing forms resembling coral. 



Crystalline aggregate. An aggregate of imperfect crystals. 



Cube. An isometric form bounded by six rectangular faces. In ideal 

 crystals the faces are square. 



Dendritic. See Arborescent. 



Dihexagonal. Presenting in section, a 12 sided symmetric figure closely 



related to a hexagon. [See p. 26, fig. 98] 

 Diploids. Isometric forms bounded by 24 four sided faces. The diploid 



is so named from the fact that the faces are grouped ,in pairs. 

 Ditetragonal. Presenting in section an eight sided symmetric figure 



somewhat resembling an octagon but more closely related to a square. 



