MINERALOGY. 



531 



Oryctogno- External Character!. Principal colour white. Sur- 



* face of the cleavage strongly iridescent. Occurs raas- 



^"""Y < ' sive, and disseminated ; massive varieties are composed 



of straight and curved lamellar distinct concretions, 



with feebly streaked splendent pearly surfaces. The 



following are the secondary forms : 



1. Rectangular four-sided prism, sometimes so low 

 mi to appear tabular, and resemble a cube. The prece- 

 ding figure truncated on all the angles : when the trun- 

 cating planes become so large that they touch each 

 other, the prism appears acuminated with four planes, 

 which are set on the lateral edges, and the apex of the 

 acumination truncated. 3. The rectangular four-sided 

 prism, in which all the lateral edges are truncated, thus 

 forming an eight-sided prism ; sometimes the eight so- 

 lid angles of this figure are truncated. 4. The rectan- 

 gular four-sided prism bevelled on all the edges, or on- 

 ly on some of them : sometimes one of the bevelling 

 planes is awanting, when the edge appears to be only 

 obliquely truncated. 5. Slightly oblique four-sided 

 pri>m. Formed when the truncating planes of No. 9. 

 become so large that the original planes disappear. 6. 

 Rectangular four-sided prism, in which the angles are 

 truncated, and the edges bevelled. 7- Rectangular four- 

 tided table, hi which the two opposite broader terminal 

 planes are doubly bevelled, and the two smaller planes 

 very flatly acuminated with four planes, of which two 

 are set on the lateral planes, the other two on the ter- 

 minal planes, and the terminal edges bevelled. 



Crystal* very small, small, middle-sized, and very 

 rarely large. The surface of the crystals N'os. 1, 2. and 

 4. is smooth ; the surface of Nos. 3. and 5. and the acu- 

 minating planes of No. 7- are longitudinally furrowed ; 

 the bevelling planes of No*. 4. 6. and 7. are transverse- 

 ly streaked. All the other planes of the secondary cry- 

 tals are smooth. The middle point of the end of the 

 crystals isoften concave Lateral planes occasionally bul- 

 ging, and the terminal planes rose-like. Externally 

 iplendent ; but only the terminal planes of the prism 

 pearly. Fracture small and perfect conchoidal, and the 

 lustre glistening and vitreous. Semitransparent, pass- 

 ing into transparent, and into translucent. Refracts 

 tingle. 



Chemical Character*. It exfoliates rery readily be- 

 fore the blowpipe, (it even exfoliates when held in the 

 flame of a candle,) and melts easily into a white-colour- 

 ad enamel. 



Myiical Characters. It becomes feebly electric by 

 rubbing. 



ApophylliW of Utfo. 



Cm*. Part* Silica, . 52.00 

 Lime, . 24.50 



Potash, . 8.10 

 \\ater, 13.0099.60, Rose. 



Geognostic and Geographic Situation* It occurs in 

 the secondary trap-rocks of the island of Sky : in rocks 

 of the same description in the Faroe islands ; in the 

 island of Disco in West Greenland, and on the main- 

 land of Greenland. One of the earliest known localities 

 of this mineral is the island of L'ton, not far from Stock- 

 holm, whereit occurs in beds of magnetic-ironstone, along 

 with common felspar, calcareous-spar, and hornblende. 



w ea '*- WAYELLITE, Jameton. 



External Characters. Colours greyish-white, green - 

 ish-white, ash-grey, asparagus-green, and sometimes 

 spotted-brown. Occurs botryoidal, globular, stalacti- 

 tic ; and these forms are composed of fibrous or fine 



prismatic distinct concretions, which are scopiform or Orjctogno- 

 stellular ; sometimes these prismatic concretions are , * 

 collected into granular, and both are occasionally tra- ^~ "i 1 """"" 

 versed by lamellar concretions. Occurs crystallized in 

 the following figures : 



1. Very oblique four-sided prism, flatly bevelled on 

 the extremities, the bevelling planes set on the obtuse 

 lateral edges. 2. The preceding figure very deeply trun- 

 cated on the obtuse lateral edges. Cleavage prismatic. 

 Externally shining : internally shining, passing into 

 splendent ; and lustre pearly. Translucent. Hardness 

 = 3.54.0. Sp. gr. 2.270, Lucas. 2.22, 2.253, Gre- 

 gor 2.25, 9.4, Aitken. 



Chemical Characters. It becomes opaque and soft by 

 the action of the blowpipe, but nether decrepitates nor 

 fuses. By the aid of heat it is soluble in the mineral 

 acids and fixed alkalies, with effervescence, and leaves 

 very little residue. 



Constituent Part*. 

 Bamstaplc WtTcIlite. 



Alumina, 71.50 70.0 Alumina, 



Oxide of iron, 0.50 I'hojphoric acid, 



I-ime, . l.t Fluoric acid, 



Wattr, - W.O t6.t Lime, 



^ Iron and Manganese, 



100 97.6 Water, 



KUp. Brit, na-.-ii. NichoL 

 b. ir. i. \10. Jouro. xii. 1 J7. 90.36 



Bttzrlui,, 



From this analysis of Berzelius, wavellite appears 

 to be hydrous phosphat of alumina. 



Geognottic and Geographic Situations. This mineral 



occurs in veins, along wath fluor-spar, quartz, tinstone, 

 and copper-pyrites, in granite, at St. Austle in Corn- 

 wall. At Barnstaple in Devonshire, where it was first 

 found by Dr. Wavell, it traverses slate-clay in the form of 

 small cotemporaneous veins. The Secretary of the Wr- 

 nerian Society, Mr. Ncill, found it in a similar situation 

 in Corrivelan, one of the Shiant Isles, in the Hebrides. 



GENUS VII. FELSPAR. Fctsrxs. 



Rhomboidal, pyramidal, prismatic. Imperfectly axi- 

 frangible. Hardness = 5.0 (i.O. Sp. gr. = 2.5 

 2.8. 



I. RHOMBOIDAL FELSPAR, or NEPHEMNE, Jame- tthomboi- 

 tttn. Rhomboedrischer Feldspath, Motif. Nepheline, dal Fe!- 

 Hauif tnd Wcnter. spar. 



Di-rhomboid = 152* 44'; 56 15'. Cleavage is four- 

 fold. Three of the cleavages are parallel with the 

 lateral planes, and one with the terminal planes, of the 

 six-sided prism. Hardness = 6.0. Sp. gr. = 2.5 2.6. 



External Characters. Colours white and grey. Oc- 

 curs massive and crystallized. The secondary forms 

 are the following : 



1. Perfect equiangular six-sided prism. 2. The prece- 

 ding figure, truncated on the terminal edges. S. Thick 

 ix-sided table, in which the lateral edges are truncated. 



Externally crystals splendent: internally shining, 

 and lustre vitreous. Fracture conchoidal. Strongly 

 translucent, passing into transparent. 



Chemical Characters. It melts with difficulty before 

 the blowpipe into a dark glass. 



Const. Parts. Silica, . 46 



Alumina, . 49 

 Lime, . 2 



Oxide of Iron, 1 y8,Vauquelin. 



Geognosiic and Geographic Situation*. It occurs in 

 drusy cavities in granular limestone, along with ceyla- 

 nite, vcsuvian, and meionite, at Monte Somma, near 



2 



