106 



Hemi-cry.'itain72e.—A\:)]Aied to an igneous rock which consists partly of 

 non-crystalline material. 



Holo-c7-ystaUine. — Applied to an igneous rock which is composed entirely 

 of definitely crystalline minerals. 



Igneous Bocks. — Those formed by the fusion of pre-existing rocks. 



Impregnation. — A term applied when secondarj' minerals are disseminated 

 through the mass of a rock. 



Lava. — Rock that has flowed from a volcano at the surface of the earth. 



Lead. — See page 27. 



Malleahility. — The pi'operty possessed by some minerals of flattening 

 without crushing when hammered. 



Massive. — Applied to minerals which, while being truly crystalline in 

 structure, do not show any external crystal form. 



il/e?ajj%re. -^Basalt that has been highly altered with the production of 

 secondary minerals. 



Metamorpliism. — The oDcration of agencies such as fii'essure, whereby 

 rock masses entirely lose ::heir original characteristics. 



Octahedron. — A cryt-tal form, consisting of a double four-faced square 

 pyramid, the edges o-fltpwrloh are all equal in length. See page 74. 



Oolitic. — A structure in rocks, occurring particularly in limestones, 

 whereby they resemble the roe of a fish. 



Pegmatite. — A coarsely crystalline rock, consisting essentially of quartz 

 and felspar, frequently found in veins traversing granite. 



PisoUtic. — Similar to oolitic, but coarser, the granules approximating to 

 peas in size, 



Porphyritic. — Applied to an igneous rock contains crystals of con- 

 spicuously large size. 



Pseudomorphism. — The replacement of one mineral substance by another. 



Pyrite. — The usual abbreviation for iron pyrites. 



Phombic dodecahedron. — See page 151. 



Ruby Silver. — Applied to certain silver ores, consisting of silver combined 

 with sulphur and antimony or arsenic, that have a ruby appearance. 



Saccharoidcd. — Sugary in appearance. 



Schistose. — Slaty in structure. 



iSecoKcZary. —Applied to minerals and structures developed in rocks 

 subsequent to their formation. 



Sectility. — A property possessed by certain minerals whereby they may 

 be cut with a knife. 



