AMI 



[19] 



A M M 



specimens come from India, Spain, 

 and Siberia, but the amethyst is 

 commonly found in most countries. 

 The amethyst is a transparent gem 

 of a purple or violet-blue colour; it 

 is sometimes found naturally colour- 

 less, and may at any time be made 

 so by putting it into the fire. 

 When deprived of its colour, it 

 greatly resembles the diamond. 

 Some derive the name amethyst 

 from its colour, which resembles 

 wine mixed with water ; whilst 

 others, with more probability, 

 think it obtained its name from 

 its supposed virtue of preventing 

 drunkenness ; an opinion which, 

 however imaginary, prevailed to 

 that degree among the ancients, 

 that it was usual for great drinkers 

 to wear it about their necks. It 

 occurs massive, in rolled pieces, 

 in angular pieces, and crystallized. 

 In the massive specimens several 

 colours occur together. Its charac- 

 ters generally are those of common 

 quartz. According to Rose, it con- 

 tains silex 97*50, alumine 0*25, 

 oxide of iron 0'50, oxide of man- 

 ganese 0*25. The oriental amethyst 

 is a sapphire ; the green variety is 

 the chrysolite of some authors. 



AMETHY'STINE. Possessing the pro- 

 perties of an amethyst ; of the 

 colour of an amethyst. 



A'MIANTH. ] famiante, Fr. ctmianto, 



AMIANTHUS, j It.) A variety of as- 

 bestos, or flexible asbestus ; an 

 incombustible mineral composed of 

 very delicata and minute fibres, 

 which were sometimes, according 

 to Dioscorides, worked into a cloth 

 capable of resisting the action of 

 fire. It is unctuous to the touch ; 

 has a shining or silky lustre ; and 

 is slightly translucent. Although 

 in mass it fuses with difficulty, 

 when in single fibres it melts in 

 the flame of a lamp. 



AMIA'NTHIFOEM. Having the form or 

 likeness of Amianthus. 



AMIANTHOID. A variety of asbcsti- 

 form actinolite, so named by Haiiy. 

 See Asbestiform actinolite. 



AMMONA'CEA. According to the ar- 

 rangement of De Blainville, a 

 family of the order Polythala- 

 macea. It embraces the genera 

 Discorbis, Scaphites, Ammonites, 

 and Simplegas. In the Lamarckian 

 system the ammonacea is a family 

 of the order Polythalamous cephal- 

 opoda, embracing the genera Am- 

 monites, Ammonoceras, Baculites, 

 and Turrilites. 



AMMONIA, or Volatile alkali, when 

 pure, is in a gaseous form. It 

 consists of hydrogen and nitrogen, 

 in the proportions of 1-76 of hy- 

 drogen, and 98*24 of nitrogen,. 



AMMONELLIPSI'TES. A genus of fossil, 

 multilocular, flatly discoidal, and 

 eiliptically spiral shells ; the turns 

 contiguous and apparent on both 

 sides; the chambers separated by 

 winding septa ; the siphuncle mar- 

 ginal. Parkinson. 



A'MMONITE. (from Jupiter Ammon.} 

 An extinct and very numerous 

 genus of the order of molluscous 

 animals called Cephalopoda, allied 

 to the modern genus Nautilus, 

 which inhabited a chambered shell, 

 curved like a coiled snake. Species 

 of it are found in all geological 

 periods of the secondary strata ; 

 but they have not been seen in the 

 tertiary beds. They are so named 

 from their resemblance to the horns 

 on the statues of Jupiter Ammon. 

 Lyell. 



One hundred and seventy-three 

 species are mentioned as having 

 been discovered in the oolitic group, 

 and upwards of three hundred have 

 been described. The ammonites 

 are a genus of shells of the class 

 of univalves, the characters of 

 which are a discoid spiral, with 

 contiguous turbinations all ap- 

 parent, and the internal parieties 

 articulated by sinuous sutures ; 

 they have also transverse parti- 



