Bryctogno- in which the bevelling planes are set on the smaller 



7- lateral planes, and the edge of the bevelment is slightly 



*"" nr~ ' truncated. Externally crystals almost always shining. 



Internally shining, or glistening, and pearly. Fracture 



fine-grained uneven. Alternates from translucent, 



through semi-transparent into transparent. Rather 



easily frangible. 



Chemical Characters. It intumesces before the blow- 

 pipe, and melts into a pale green or yellow, or green- 

 ish-black frothy glass, but does not gelatinate with 

 acids. 



Physical Characters. According to the observations 

 of M. De Dree, it becomes electric by heating. 

 Constituent Parts. Silica, . 48 



Alumina, . 24 



Lime, . . 23 

 Oxide of Iron, 499 



Pauquelin. 



Geognoslic and Geographic Situation. It occurs in 

 veins in primitive and secondary rocks, in France, 

 Tyrol, Greenland, and Cape of Good Hope. 



SECOND SUBSPECIES. 



p n > 



Jameson Fasriger Prehnite, 



Jameson. Prismatischer Oryctogoo - 



sy. 



FIBROUS PREIIMTC, 

 Werner. 



External Characters. Colours green and green- 

 ish white. Occurs massive, reniform, in straight 

 scopitbrm and stellular fibrous, and radiated distinct 

 concretions, which are collected into large and coarse 

 angulo-granular concretions ; also crystallized in acicu- 

 lar tour-sided prisms. Internally glistening; lustre 

 pearly. Translucent. Easily frangible. 



Chemical Character. Before the blowpipe it melts in- 

 to a vesicular enamel. 



Physical Character. It becomes electric by heating. 



MINERALOGY. 527 



1. PIIISMATIC DATOLITE, 



Datholit, Muhs. 



Prism = 109 28'. Cleavage the same. 

 This species is divided into two subspecies, viz. Com- 

 mon Datolite, and Botryoidal Datolite. 



FIRST SUBSPECIES. 

 COMMON DATOLITE, Jameson. Datholit, Werner. Common 



External Characters. Colours white, and grey, which Datollte - 

 latter inclines to celandine-green, and rarely to muddy 

 honey-yellow. Occurs in massive portions, which are 

 divided into large coarse and small granular distinct 

 concretions ; crystallized. The principal secondary 

 forms are the following: 



1. Low oblique four-sided prism. 2. Rectangular 

 four-sided prism, flatly acuminated on the extremities, 

 with four planes which are set on the lateral planes. 



Externally shining. Internally intermediate between 

 shining and glistening, lustre resinous. Fracture in- 

 termediate between fine-grained uneven and imperfect 

 conchoidal. Translucent, and sometimes transparent. 

 Very brittle. Difficultly frangible. 



Chemical Characters. When exposed to the flame 

 ofa candle, it becomes opaque, and may then be easily 

 rubbed down between the fingers. Before the blow. 

 pipe, it intumesces into a milk-white coloured mass, 

 and then melts into a globule of a pale rose-colour. 



42.50 

 28.50 

 80.40 



0.75 



3.00 



2.0097.15 



ATOI.ITE. 



('onitit. Parts. Silica, 



Alumina, 



Lime, 



Natron and Potash, 



Oxide of Iron, 



Water, 



Laugier, Annales du Museum, t. xv. p. 205. 

 Geognottic Situation. This subspecies appears to 

 be confined to secondary mountains ; at least it has 

 hitherto been found only in secondary trap rocks, as 

 basalt, amygdaloid, basaltic-greenstone, and common 

 greenstone. It occurs either in cotemporaneous veins, 

 or in amygdaloidal, and other shaped cavities in these 

 trap rocks. 



Geographic Situation. In Scotland, it occurs in 

 veins and cavities in trap-rocks near Beith in Ayr- 

 shire ; Bishoptown in Renfrewshire ; also at Hart- 

 field, near Paisley; near Frisky Hall, in Cockney 

 Burn, Old Kilpatrick, and Loch Humphrey in Dun- 

 bartonshire ; in Salisbury Craig, the Castle Rock, and 

 Arthur Seat near Edinburgh ; in Berwickshire ; and 

 in the Islands of Mull and Raasay. 



GENUS V. DATOLITE . 

 Dattel Spatb, Mo/i*. Esmarkite, Hautmann. 



Three axes. Cleavage prismatic, but detected with 

 difficulty. Internally, lustre resinous. Not blue. Hard. 

 ness = 5.05.5. Sp. gr. = 2.9 3.0. 



This genus contains one species, TJZ. Prismatic Da- 

 tolite. 



Conslit. Parts. Silica, . . 37.0 



Lime, . . 28.0 



Boracic Acid, . 31.0 

 Alumina, . . 1.0 



Iron, Manganese, and 



Nickel, . 1.5 



Water, . . 1.4100 



Esmark. 



Geognostic and Geographic Situation. It is associat- 

 ed with calcareous-spar, more rarely with fluor-spar, 

 quartz, and sometimes prehnite, in a bed of magnetic 

 ironstone in gneiss, at the mine of Nodebroe, near 

 Arendal in Norway. It is said also to occur in small 

 veins in greenstone, ia the Geisalp in Sonthofen ; and 

 in the Syseralp. 



SECOND SUBSPECIES. 



BOTRYOIDAL DATOLITE or BOTRYOLITE, Jameson Botryoidal 

 Botryolith, Hautmann. Datolite. 



This subspecies is divided into two kinds, viz. Fibrous 

 Botryolite, and Earthy Botryolite. 



F irtt Kind. 

 FIBROUS BOTRYOLITE, Jameson. Fasriger Botryo- pibrout 



lith, Hausmann. 



External Characters. Externally grey; internally 

 white, which passes into pale rose-red. The colours 

 are in concentric stripes. Occurs reniform, botryoidal, 

 small globular ; in fibrous concretions which are sco- 

 piform and stellular ; these concretions are again col- 

 lected into granular concretions, which are traversed 

 by very thin curved lamellar concretions. Surface 

 granulated or rough, and dull. Internally glimmer- 

 ing and pearly. Fracture splintery. Translucent on 

 the edges. 



Geognoslic and Geographic Situations. It occurs in 

 the Kjenlie mine, near Arendal in Norway, along with 

 common quartz, schorl, calcareous spar, and iron-py. 

 rites, in a bed of magnetic ironstone, in gneiss. 



B troy lite. 



The , 



cTtH M. Fssnsrt 



lutoSfc refcn to the granular concretions which this rpeciw exhibit, in the mature varietiei, and wu given to it by iu di<- 



