530 



Oryctogno- Constituent Parts. Silica, 

 y- Alumina, 



'*^Y"*' Lime, 



Soda, 

 Water, 



MINERALOGY. 



54.46 

 19-70 



1.61 

 15.09 



9.83100.63 



Natrolitc. 



Gehlen in Schweigger's Journ. viii. 355. 

 SECOND SUBSPECIES. 



NATROLITE, Jameson. Natrolith, Werner. 

 External Characters. Colours yellow, yellowish- 

 brown, or yellowish-white. Colours generally arranged 

 in narrow striped delineations, which are parallel with 

 the reniform external shape. Occurs massive, in plates, 

 and reniform ; also in distinct concretions, which are 

 fibrous, granular, and lamellar ; the fibrous are straight, 

 and scopiform or stellular ; these are collected into 

 large and coarse granular, and both are intersected by 

 curved lamellar concretions. Internally glistening, pass- 

 ing into glimmering, and lustre pearly. Fracture not 

 visible. Translucent on the edges. 



Chemical Characters. Before the blowpipe it becomes 

 first black, then red, intumesces, and melts into a white 

 compact glass. 



Constituent Parts. Silica, . . 48.00 

 Alumina, . 24.25 

 Natron, . 16.50 



Oxide of iron, 1.75 



Water, . 9.0099-50 



Klaproth, Beit. b. v. s. 44. 



Geognostic and Geographic Situations. It occurs in 

 small cotemporaneous veins in clinkstone porphyry, in 

 the hills of Hohentwiel. 



THIRD SUBSPECIES. 



Mealy zeo- MEALY ZEOLITE, Jameson. Mehlzeolith, Werner. 

 li te . External Characters. Colours white and red. Oc- 



curs massive, reniform, coralloidal, sometimes it forms 

 a crust over the other subspecies of zeolite, or is 

 disposed in delicate fibrous concretions. Internally 

 dull, or very feebly glimmering. Fracture coarse 

 earthy. Opaque. Mass very soft, but the individual 

 parts as hard as fibrous zeolite. Uncommonly easily 

 frangible. Feels rough and meagre ; and when we 

 draw our finger across it, it emits a grating sound. 

 Sometimes so light as nearly to swim in water. 



Chemical Characters. It intumesces before the blow- 

 pipe, and forms a jelly with acids. 



Const. Parls.-~ Silica, . . 60.0 



Alumina, . . ' 15.6 



Lime, . . 8.0 



Oxide of iron, . 1.8 



Loss, by exposure to heat, 1 1.6 97 

 Hisinger's Af handlingar i Fysik, &c. th. 3. 

 Geognostic Situation. It occurs in similar reposito- 

 ries with the other subspecies. 



Geographic Situation. It is found near Tantallon 



Castle in East Lothian, in the islands of Sky, Mull, and 



Canna, also in the Faroe Islands, Iceland, and Sweden. 



Prismatoi 7- PHISMATOIDAL ZEOLITE or STILBITE, Jameson. 



dal zeolite. Prismatoidescher Schaumspath, Mohs. Stilbite, Hauy. 



Prism = 99" 22'. Cleavage in the direction of the 



smaller diagonal very distinct. Hardness =r 3.54.0. 



Sp. gr. = 2.02.2. 



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

 liated Zeolite, and Radiated Zeolite. 



FIRST SUBSPECIES. 



FOLIATED ZEOLITE, Jameson. BKitter-Zeolith, Werner. 



External Characters Colours white, red, yellowish- 

 grey, and pinchbeck-brown. Occurs massive, dissemi- 

 nated, globular, in amygdaloidal-shaped pieces ; also in 



Foliated 

 zeolite. 



distinct concretions, which are large, coarse, and small Oryctogno- 

 angulo-granular ; seldom thin and curved lamellar, _'* l 

 which are again collected into granular. Frequently ""V 

 crystallized, and the following secondary forms occur : 

 1. Low, oblique, sometimes rather broad, four-sided 

 prism. 2. Low six-sided prism. 3. Eight-sided prism. 

 Lateral planes of the prisms are transversely streak- 

 ed, the terminal planes smooth. Planes sometimes 

 shining, sometimes splendent, and the lustre vitreous. 

 Internally alternates from shining to splendent, and the 

 lustre pearly : the pinchbeck-brown has a semi-metal- 

 lic lustre. Fracture conchoidal. Massive varieties are 

 strongly translucent: some varieties, particularly the 

 pinchbeck-brown, are only translucent on the edges ; 

 but the crystals are generally semitransparent and tran- 

 sparent. Refracts single. 



Chemical Characters. It intumesces and melts before 

 the blowpipe, and during its intumescence emits a 

 phosphoric light. It does not form a jelly with acids. 

 Constituent Parts. Silica, . 52.6 



Alumina, . 17.5 



Lime, . . 9.0 

 Water, . 18.597.0 



Vauqtielin, Jour, de Mines, N. xxxix. p. 164. 

 Geognostic Situation. It occurs principally in secon- 

 dary amygdaloid, either in drusy cavities, along with cal- 

 careous-spar and calcedony, or in cotemporaneous veins. 

 It is also met with in primitive and transition mountains. 

 Geographic Situation. In Scotland it occurs in drusy 

 cavities or veins in the secondary trap-rocks that 

 abound in the middle division of the country. Very 

 beautiful specimens of the red foliated and radiated 

 zeolites are found at Carbeth in Stirlingshire, and at 

 Loch Humphrey in Dunbartonshire ; and the same va- 

 rieties occur on the coast between Bervie and Stoneha- 

 ven in Angus-shire ; also in the secondary trap-rocks 

 of the Hebrides, as of Canna, Skye, and Mull. In the 

 north of Ireland it is an inmate of secondary trap-rocks. 



SECOND SUBSPECIES. 



RADIATED ZEOLITE, Jameson. Strahl Zeolith, Werner. Radiated 

 External Characters. Occurs almost always white ; zeolite, 

 sometimes grey, yellow, flesh-red, and blood-red. Is 

 found massive, in angular pieces, and globular ; also in 

 distinct concretions, which are prismatic and granular : 

 the prismatic are broad and narrow scopiform, and stel- 

 lular, and are collected into large, coarse, and small 

 angulo granular concretions. Frequently crystallized. 

 Primitive figure the same as that of foliated zeolite ; 

 and it exhibits the following secondary forms : 



1. Broad rectangular four-sided prism, rather acutely 

 acuminated on both extremities by four planes, which 

 are set on the lateral edges. 2. Sometimes No. 1. is so 

 thin, that it may be considered as a long six-sided ta- 

 ble, bevelled on the shorter terminal planes. 



The broader lateral planes of the crystals are smooth, 

 the smaller longitudinally streaked, and the acumina- 

 ting planes smooth or rough. The surfaces of the broad- 

 er lateral planes of the crystals, No. 1, 2. are splendent 

 and pearly : the other planes shining and vitreous : in- 

 ternally the lustre more or less shining and pearly. Cry- 

 stals strongly translucent, sometimes passing into semi- 

 transparent. Hardness same as foliated zeolite. Brit- 

 tle. Easily frangible. 



Its Geognostic and Geographic Situations are the 

 same as those of Foliated Zeolite. 



8. AxiFRANGIBLE ZEOLITE or APOPHYLLITE, Jame- Axifrangi- 



son Fishaugenstein, Werner. Apophyllite, Haiiy. lie zeolite, 



Ichthyophthalm, Karsten. 



Pyramid unknown. Cleavage very distinctly axi- 

 frangible. Hardness = 4.55.0. Sp. gr. = 2.22.5. 



