M I N E R A L G Y. 



529 



PyramiJal 

 Zeulitr. 



where it is often associated with agate, calcareous- spar, 

 seolite, and green-earth. 



Geographic Situation -- The vesicular cavities of 

 the trap-rocks of Mull and Skye afford crystals of 

 chabasite ; it occurs- in similar rocks in the north of 

 Ireland ; and beautiful specimens are found in the 

 amygdaloid of Iceland and of the Faroe Island?. 



4. PYRAMIDAL ZEOLITE, or CROSS-STONE, Jameson. 

 Pyramidischer Schaum Spath, Mohs. Kreutstein, H 'tr- 

 uer. Harmotome, Hmiy. 



1'y ramid= 121 58', 86 36'? Cleavage is either pyra- 

 midal, or is in the direction of the diagonals. Hard- 

 = 4.5. Sp. gravity=2.3, 2.4. 



External Characters. Colours white, grey, yellow, 

 and red. Occurs very rarely massive ; most frequently 

 crystallized. The following are the principal secondary 

 forms which have been observed: 1. Broad, seldom 

 equilateral, rectangular four-sided prism, rather acutely 

 acuminated on the extremities with four planes, which 

 are set on the lateral edges. 2. Twin-crystal, which 

 h formed by two crystals of No. 1. intersecting each 

 other, in such a manner that a common axis and acu- 

 mination is formed, and the broader lateral planes make 

 four re-entering right angle;. The surface of the 

 smaller lateral planes is double plumosely streaked, the 

 broader lateral plane* transversely streaked, and the 

 acuminating planes streaked parallel with the smaller 

 lateral planes. Internally glistening, and the lustre in. 

 tci mediate between vitreous and pearly. Fracture small 

 and perfect conchoidal, passing into uneven. Translu- 

 cent, sometimes passing into semitransparent. 



Chemical Characters Before the blowpipe it exhi- 

 .1 greenish-yellow phosphorescence, and then melts 

 with intumescence into a colourless glass. 



Constituent Parlt Silica . 49 



Alumina . 10' 



Baryta . 18 



Water . 1598 



Klap. Beit. b. ii. s. 83. 



z'irtitic and Geographic Situation. It has been 

 hitherto found only in mineral veins and in, agate balls. 

 At Andreasberg in the Hartz, it occurs in veins that 

 traverse clay-slate and greywacke rocks, along with ga- 

 lena or lead glance ; at Kongaberg in Norway, in veins 

 containing native silver, ores of silver, lead, zinc, arse- 

 nic, and iron ; and Strontian in Argyleshirc, in galena 

 veins that traverse gneiss. At Obcrstein it occurs in 

 gate balls, in trap rocks, and in a similar situation near 



. illage of Old Kilpatrick in Dunbartonshire. 

 nru- 5. DIPHISMATIC ZEOLITE, or L\t MONITE, Jaxinon. 

 nc Zrolitr. Di-prismatischerSchaumSjiatli.. A/O/I.I. Lomonit,/rrrn?r. 



\trtic;d prism = 90 12'; horizontal prism in the 

 direction of the smaller diagonal 121 34.' Cleavage 

 double. Hardness = 5. Sp. gr.=2.3 2.4. 



External Characters Colours yellowish- white, snow- 



white, nnd greyish-white. Occurs in massive forms, 



arranged in large and coarse granular distinct concre- 



: also crystallized. Internally sometimes shining, 



sometimes glistening, and lustre pearly. When in a 



. state is transparent, but on exposure to the atmo- 



sphere, it very soon becomes opaque. When fresh, is ra- 



ther harder than fluor spar ; but on exposure to the atmo- 



sphere, it soon becomes so soft as to yield to the mere 



ure of the finger. Uncommonly easily frangible. 



(.'hfmical Characters. It forms a jelly with acids. 



Const. Parlt, Silica, 



Alumina, 

 Lime, 

 Water, 

 Carbonic acid, 



VOL. XIV. PART It. 



94.0 

 22.0 



9-0 

 17.5 



2.5100 Vogel. 



Geognottic and Geographic Situations. This mineral Orjctogn - 

 was first found in the year 1785, in the lead-mines of S T- 

 Huelgoet in Brittany, by M. Gillet Laumont, a distin- ""V 

 guished French mineralogist. Since that period, it has 

 been discovered in other parts of the world, as in Scot- 

 land, Ireland, Faroe Islands, &c. 



6. PRISMATIC ZEOLITE or MESOTYPE, Jameson. Prismatic 

 Prismatischer Schaum Spath, Mohs. Mesotype, Haity. Zeolite. 



Prism 91 25'. Cleavage the same. Hardness=5.0 

 5.5. Sp. gr.=2.02.3. 



This species is divided into three subspecies, viz. 

 Fibrous Zeolite, Natrolite, and Mealy Zeolite. 

 FIHST SUBSPECIES. 



FIBROUS ZEOLITE, Jameson. FasrigerZeolit,'F<?rwr. Fibrous 



This subspecies is divided into two kinds, viz. Aci- Zeolite, 

 cular or Needle Zeolite, and Common Fibrous Zeolite. 

 First Kind. 



ACICULAH or NEEDLE ZEOLITE, Jameson. Nadelzeo- Acfcuiar 

 lith, Werner. or NeedU 



External Characters. Colours greyish or yellowish- Zeolite, 

 white, and frequently reddish- white. Occurs massive, 

 antl in distinct concretions ; these are prismatic ami 

 granular ; the prismatic are thin, sometimes passing in- 

 to fibrous, straight, ami scopiform; the granular include 

 the prismatic, and are large and coarse. It also occurs 

 crystallized, and the following are the secondary figures : 



1. Acicular rectangular four-sided prism, very flatly 

 acuminated, with four ]il.inr, which are set on the la- 

 teral planes. 2. The prism truncated on the edges. 



Lateral planes of the crystals are longitudinally 

 streaked, but the acuminating planes are smooth. Ex- 

 ternally the crystals are shining, passing into splendent. 

 Internally glistening, and lustre vitreous, inclining to 

 pearly. Fracture small and fine-grained uneven. Trans- 

 lucent ; crystals semitransparent and transparent ; and 

 it refracts double. 



Chemical Characters It intumesces before the blow- 

 pipe, and forms a jelly with acids. 



Physical Characters. It becomes electric by heating, 

 and retains this property some time after it has cooled. 

 The free extremity of th'e crystal, with the acumination, 

 shews positive, and the attached end negative electrici- 

 ty. I f any. 



Constit. Part*. Silica, . . 50.2* 

 Alumina, . 29-30 



Lime. . . 9-46 



Water, . . 10.0099.00 

 Vatiquelin, Jour, des Mines, N. 44. p. 576. 



Geognostic and Geographic Situations. It occurs in 

 secondary trap rocks, as in basalt, greenstone, and a- 

 mygdalo'id. In this country it occurs near the vil- 

 lage of Old Kilpntrick, Dunbartonshire, also in Ayr- 

 shire and Perthshire, and always m trap-rocks. 

 Second Kind. 



COMMON FIBROUS ZEOLITE, Jameson. Cemeincr Common 

 Faser Zeolith, Werner. Fibroui 



External Character** Colours white, red, yellow, Zeolite. 

 nnd yellowish-brown. Occurs massive, in blunt-angu- 

 lar pieces, in balls, and small reniform, and these forms 

 are composed of distinct concretions, whirh ;ue fibrous 

 and granular. The fibrous concretions are thin, straight, 

 scopiform, and stellular ; the granular, which include 

 the fibrous, are large and coarse longish or nngulo-gra- 

 nular, and are very much grown together. Occurs in 

 capillary crystals. Internally it is strongly glimmering, 

 passing into glistening, and lustre pearly. Faintly 

 translucent. Its geognostic and geographic situations 

 are the same with needle zeolite. 



Chemical Characters. It intumesces before the blow, 

 pipe, and forms a jelly with acids. 

 3x 



