MINERALOGY. 



459 



often longer than the lateral ones, as in ma- Oryetogne. 



lachite, fibrous zeolite, and reniform, red he- ^ *> ^, 



rnatite. 



y. Promiscuous Jibrous, when the fibres cross each 

 other in all directions, as in compact plumos 

 antimony. 



D. Radiated fracture. The distinct concretions in this 

 kind of fracture, have two discernible dimensions, 

 namely, in length and breadth, and of these the first 

 is the most considerable. Hence the fracture sur- 

 face exhibits long and narrow fracture parts, which 

 sometimes rest on each other, or are placed side by 

 side. The lustre alternates from splendent to shin- 

 ing, and the transparency from translucent to opaque. 

 The minerals in which it occurs are sometimes cry- 

 stallised either in needles, or in broad prisms. In the 

 radiated fracture, we have to attend to the breadth, 

 direction, position, and cleavage of the rays, and th 

 aspect of the surface of the rays. 



a. The breadth of the rays. 



*. Uncommonly broad radiated, when the breadth 

 of the rays is more than one-fourth of an inch, as 

 it sometimes the case with radiated grey anti- 

 mony, and kyanite. 



ft. Broad radiated, when the breadth of the rays is 

 less than the fourth of an inch, but not less than 

 a line, as in common actynolitc and mica. 



y. Narrow radiated, when the breadth is even 

 leu than in the preceding, also in actynolitc. 



b. Direction of the rayt. 



. Straight radiated, which is very frequent, as in 



ctynolite. 

 ft. Curved radiated, which is rare. The curvature 



is either in the direction of the breadth, as in 



common actynolite, or in the direction of th* 



length, as in kyanite. 



c. Position of the rayt. 



. Parallel radiated, as in grey antimony, and in 



common hornblende. 

 3. Diverging radiated. 



i. Stellular, as in radiated red cobalt-ochre, or 



cobalt-bloom, 

 ii. Scopiform, u in radiated grey antimony, 



and radiated zeolite. 



y. Promiscuous, as in hornblende-slate, and grey 

 antimony. 



d. Cleavage or postage of the rayt. 



a. Single cleavage. 



b. Double cleavage, as in hornblende. In general 

 the cleavage, of which a particular account will 

 be given when treating of the foliated fractnre, 

 U imperfect, and we seldom can distinguish 

 more than one variety of it, which is the single. 



e. The atpect of the rays surface. The rays are ei- 

 ther 



. Smooth, as in radiated grey antimony and acty- 

 nolitc. 



ft. Streaked, as in radiated grey manganese-ore and 

 hornblende. 



E. Foliated fracture. This kind of fractnre is composed 

 of folia or planes in which the length and breadth. 

 are nearly equal ; which are shining or splendent, 

 and superimposed on each Trther in various direc- 

 tions. It occurs in minerals possessing every degree 



of the Genniiu ; which I bare tnailated ipKt fracture, probably no! a very appropriate translation, 

 fibroin and radiated fracture* are more properly ipeaking varieliet of diilinct concra- 



m tliu article. 



Coarse earthy and Fine earthy. It passes some- 

 times into even, and sometimes into uneven. Ex- 

 amples, Chalk, and clay ironstone. 

 f. Hackly. When the fracture surface consists of nu- 

 merous small slightly bent sharp inequalities, which 

 are sometimes only discoverable to the feel, it is 

 said to be hackly. It occurs only in native mal- 

 leable metals, and is, consequently, accompanied 

 with metallic lustre and opacity. Examples, Na- 

 tive copper, and native silver. 



These different kinds of compact fracture often 

 run into each other, and frequently several occur 

 together ; in the latter case, the most prevalent 

 fracture is that which is to be taken as the cha- 

 racteristic one. 



B. Split fracture*. Under this head we include what 



u called by tome mineralogists the Structure of 

 Mineral*. 



Three different kinds of split fracture are enu- 

 merated by authors, viz. \hejibroui, radiated, and 

 foliated. 



C, Fibrous fracture. In this kind of fracture the di*- 



tinct concretions of which it is composed are so 

 narrow, that the only magnitude which can be 

 readily determined, by the naked eye, U the length ; 

 hence it is to be considered as composed of line- 

 like parts. It is never dull; on the contrary, 

 it is generally glimmering or glistening, seldom 

 thining, and never splendent. It sometimes occurs 

 in transparent minerals, but oftener in those which 

 are only translucent, or even nearly opaque. The 

 minerals in which it occurs are sometimes crys- 

 tallised in capillary crystals. In the fibrous frac- 

 ture we have to attend to the thickness, the direc- 

 tion, and the petition of the fibres. 

 a. Thickness of the fibres. 



. Coarse fibrous, when the fibres are of considerable 

 thickness, as in common fibrous quartz, common 

 abestus, and fibrous gypsum. 



A. Delicate Jibrous, when the fibres are narrower than 

 in the preceding variety, and occasionally so 

 delicate, a* to be scarcely visible to the naked 

 eye. Examples of delicite fibrous fracture oc- 

 cur in red hematite, and fibrous malachite ; and 

 of extremely delicate fibrous fracture, in c.ilc- 

 sintcr and amianthus. 



The coarse fibrous fracture is the link which 

 connects the fibrous with the radiated fracture. 

 b. The direction of the fibres. 



. Straight fbrout, a* in red hematite and fibrous 



malachite. 



d. Curved Jilrous, as in asbestiu and fibrous gypsum. 

 . The petition. 



*. Parallel Jibrout, when the fibres, whether straight 

 or curved, are parallel to each other, as in com- 

 mon asbestus, and fibrous gypsum. 

 . Diverging Jibroui, when the fibres proceed from a 

 common centre, in different directions ; and this 

 is either 



i. Stellular diverging, when the fibres diverge in 

 all directions, like the radii of a circle, as in 

 brown hematite. 



ii. Fatcicular or tconiform, when the fibres diverge 

 only on one side, so that the middle fibres are 



TkisiiUM 

 boil do D<X 



