341 



ATYLUS. 



AUGITE. 



342 



A'TYLUS, a genus of Crustaceous Animals, thus characterised by 

 Leach : 



Antenna! composed of four joints, the last of which is formed of 

 several minute articulations : upper onea rather shortest, with the 

 second joint longer than the 

 third ; under ones with the 

 second joint rather shorter 

 than the third. 



Eyes slightly prominent, 

 inserted on a process be- 

 tween the upper and lower 

 antenme. 



Legs fourteen ; first and 

 second pair furnished with 



a small compressed hand, At 'J'" s """>> 



which has a moveable thumb ; the other pah's having only a simple 

 claw. 



Tail, on each side, with a triple series of double styles ; upper part 

 on each side armed with a small spine or style. 



Body (including the head) composed of twelve joints. Example 

 Afylua carinatus (Gammarus carinatus, Fabr.). 



AUCHE'NIA, a genus of Ruminating Mammalia. [LLAMA.] 



AU'CUBA, a genus of plants belonging to the natural order 

 Cornaeea. Only one species is known. It is a Japanese plant, com- 

 monly cultivated in the gardens of this country as a hardy evergreen 

 shrub, remarkable for its shining pale-green leaves mottled with 

 yellow, hence sometimes called Variegated Laurel. It is described by 

 Thunberg as growing to the height of a man or higher, and as com- 

 mon in various places in Japan, both wild and cultivated. Its fruit, 

 which it bears in March, is a red berry, about the size of that of a 

 laurel, and containing a single stone, with a bitter nauseous kernel. 

 This plant is dioecious, and in this country we have only the pistilli- 

 ferous flowers. The plant, however, which is cultivated in this country 

 is only a variety : in its natural state it is said to have brownish-green 

 leaves without any blotches. 



AUGITE. The minerals to which this name has been applied 

 present us with some of the most interesting and at the same time 

 most difficult investigations that can fall under the notice of the mine- 

 ralogist and chemist, and have frequently occupied the attention of 

 the most eminent men in both sciences. Nor are these bodies 

 unworthy of such attention ; for not only would a thorough knowledge 

 of their constitution, and the relation which they bear to other mine- 

 rals, particularly to the genus JUornblende, tend much to the perfection 

 of the mineralogical system ; but, owing to their frequent occurrence 

 in nature, and from their forming one of the principal ingredients in 

 many porphyritic and trap rocks, such on the Syenite, Diallage, and 

 Schorl-Rocks, Greenstone, &c., they form a class of bodies of the 

 highest importance to the geologist. A due regard to the circum- 

 stances which are favourable to the formation of one or other of the 

 species, to the exclusion of the rest, would be likely to afford a safe 

 guide in many geological inquiries into the character and formation 

 of rocks of igneous origin. Werner was the first to divide a large 

 class of minerals occurring commonly in basalt, lavas, and other 

 volcanic rocks, into two species, to which he applied the names of 

 Augite and Hornblende. This division was founded on the difference 

 existing between the crystallised forms and structure, which, according 

 to the experience up to that time, were never associated with each 



Augite, or Pyroxene. 

 Fig. 1. 



Inclination of M on M is S7" G' 

 M on r 133' 33' 

 M on I 136' 27' 

 on 120' 57' 



s 



106' 6' 



M 



Hornblende, or Ampkibole, 

 Fig. 2. 



Inclination of M on M is 124' 31' 

 M on z 117 44' 

 P on M 103' 13' 



M 



P on 

 M 



r on r 

 r M 



- on 



104 57' 

 148" 25' 

 104 57' 



Bjr -, , Is meant the edge formed by tlie intersection of the faces s and 

 M and M, &c. 



The same division was shortly after adopted by Haiiy, who 

 applied to them the names of Pyroxene and Am^hlMf, and gave the 



measurements, determining the oblique rhombic prisms, with their 

 most general modifications characteristic of either species, which 

 however we have modified by the later measurements of Eose, 

 Mitscherlich, and Kupffer. 



Professor Mohs, however, together with Professor Jameson of 

 Edinburgh, has used the term Auyite to denote the eighth genus of 

 their respective systems, which consists of the four species designated 

 as follows : 



First species. The Oblique-Edged Auyite, corresponding with the 

 A uglte of Werner, and Pyroxene of Haiiy. 



Second species. The Straight-Edged Auyite, corresponding to 

 Hornblende and A mphibole. 



Third species. Prism ato idol Auyite, containing as sub-species the 

 minerals Epidote or Zoisite. 



Fourth species. Prismatic A ugite ; Tabular Spar or Wollastonite. 



Berzelius, on the contrary, viewing the subject in a chemical point 

 of view, has been induced to use the term Augite or Pyroxene, Horn- 

 blende or Amphibole, in the same signification as employed by Werner 

 and Haiiy. According to him, the Augites are composed of one equi- 

 valent of the bisilicate of lime united with one equivalent of the 

 bisilicate of magnesia. 



There are several varieties of this genus formed by the removal of 

 the magnesia or lime, which are replaced either by one or both of the 

 isomorphous substances the protoxide of iron, and protoxide of 

 manganese. Of these the following are the principal : 



1. IKopiidr, which may be considered as the type of the Augite 

 Genus, is readily recognised by the form of its crystal given iujig. 1, 

 and by the direction of its four cleavage planes, the most perfect 

 corresponding with the faces M, those in the direction of r and I being 

 less easily obtained ; and by its pale-green or grayish-white colour, 

 and vitreous lustre. Its hardness is 5'5, and its specific gravity is 

 3'299. Alone before the blowpipe it melts into a colourless semi- 

 transparent glass ; with borax, very readily into a transparent glass. 

 It consists chiefly of silica, lime, and magnesia, as will be seen by the 

 following analysis of a variety from Tammare by Bonsdorff : 



Silica 

 Lime 

 Magnesia 



54-83 

 2476 

 18-55 



Protoxide of Iron 



Alumina . 



Loss by heating . 



0-99 

 0-28 

 0-32 



99-73 



Several varieties, little differing from the above, are called Baclalite 

 and Faaaite, names indicative of then- locality. 



2. Hedenberyite consists chiefly of silica, lime, and protoxide of iron, 

 as may be seen by the following analysis by G. Rose of a variety from 

 Lunaberg : 



Silica 49-01 



Lime 20-87 



Protoxide of Iron 26'08 



Protoxide of Manganese with Magnesia . . . 2 -98 



98-94 

 It is of a dark-green colour, sometimes nearly black. 



3. Salilite, those varieties in which the magnesia is only in part 

 replaced by protoxide of iron, and which may be regarded as consist- 

 ing of one equivalent of Hedenbergite united with two of Diopside. 

 A variety is called Malakolith. ('Anwendung der Lothrohrs,' by 

 Berzelius.) 



4. XHallage. The difference in the analysis by Kb'hler of two speci- 

 mens, the first from Tuscany, the second from Ulthenthal in the 

 Tyrol, were as follows : 



Silica 53-20 56'81 



Lime 19-08 2-19 



Magnesia 14'91 29'67 



Protoxide of Iron . . . . 8'67 8'46 



Protoxide of Manganese . . 0.38 0'61 



Alumina 2'47 2'07 



"Water 177 Q'21 



100-48 100-02 



This variety is characterised by its mother-of-pearl lustre, and by 

 its possessing the most perfect cleavage in the direction of the diagonal 

 of the prism. It is seldom found in perfect crystals. Its most general 

 colour is a bronze yellow. 



5. Jfyperst/tme, which is very similar in its general appearances and 

 characters to Diallage, is a bisilicate of iron and magnesia. Both of 

 the last-mentioned varieties may be distinguished from the former, as 

 well as from each other, by means of the blowpipe, and by attending 

 to the following characters as stated by Berzelius : 



Zhallage alone in a matrass decrepitates, becomes of a lighter colour, 

 and gives off a little water. 



On charcoal it is with difficulty melted on the edges into a gray 

 scoria. 



With borax it is with difficulty fused into a clear glass, somewhat 

 coloured by the protoxide of iron. 



It is decomposed by the phosphate of soda and ammonia, with the 

 development of the silica. 



//!//! rtthene, on the contrary, when heated alone in the matrass, 

 decrepitates slightly, gives out a little water, but does not change its 



