ICO 



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JEW 



aceous, leathery ; latericious, re- 

 sembling bricks. 



ICOSAHE'DRAL. (from icosahedron.) 

 Having twenty equal sides or faces. 



ICOSAHE'BRON. (elicoffdcdpos, Gr. ico- 

 sedre, Pr. isosaedro, It.) A regular 

 solid, consisting of twenty triangu- 

 lar pyramids, whose vertices meet 

 in the centre of a sphere supposed 

 to circumscribe it; and therefore 

 have their height and bases equal : 

 wherefore the solidity of one of 

 these pyramids multiplied by 

 twenty, the number of bases, gives 

 the solid contents of the icosahedron. 



ICOSA'KDRIAN. (from ei'icoai and avijp, 

 Gr.) The twelfth class in Linnaeus' s 

 sexual method, consisting of plants 

 with hermaphrodite flowers, fur- 

 nished with twenty or more sta- 

 mens, inserted into the calyx. The 

 first order of this class consists of 

 trees bearing for the most part 

 stone fruits, surrounded by a pulp, 

 as the plum, peach, cherry, &c. ; 

 in the second order we find the 

 apple, pear, &c. ; in the third 

 order, the genus rosae. In this 

 class the stamens grow out of the 

 sides of the calyx, as in the straw- 

 berry, and it is important to ob- 

 serve, that such a mode of insertion 

 indicates the wholesomeness of the 

 fruit ; we are not aware that there 

 is a single exception to this rule, 

 so that a traveller, who might 

 meet with an unknown fruit, need 

 not scruple to eat it if he find the 

 stamens thus inserted. This cha- 

 racter of the insertion of the sta- 

 mens into the calyx holds good in 

 other classes, as well as in the 

 class Icosandria ; thus, in the genus 

 Ribes, including the gooseberry 

 and currant, which belong to the 

 class Pentandria, the stamens grow 

 out of the calyx, and these fruits 

 are well known to be wholesome, 

 while many of the berries of the 

 same class, whose stamens have 

 not a like insertion, are often yery 

 deleterious. 



FDOCRASE. (from Idea, form, and 

 icpaffis, mixture, Gr.) The term 

 idocrase was given to this mineral 

 by Haiiy in reference to its form, 

 which is a mixed figure. Idocrase 

 is a silicate of lime, combined with 

 a silicate of alumina. A mineral 

 found in lava, and formerly mis- 

 taken for the hyacinth; it is the 

 Yesuvian of Werner. See Vesuvian. 



JE'FFERSONITE. A mineral found in 

 New Jersey; colour olive-green, 

 passing into brown. It is named 

 after Mr. President Jefferson. 



JET. (from Gaga, a river of Asia; 

 jayet, Fr.) The Jayet of Haiiy; 

 Lignite Jayet of Brongniart ; Pech 

 Kohle of Werner. A mineral sub- 

 stance, found in detached kidney- 

 formed masses in many countries. 

 It is of a firm and very even struc- 

 ture, harder than asphaltum, and 

 susceptible of a good polish. It 

 becomes electrical by rubbing, at- 

 tracting light bodies, like amber. 

 In many respects it resembles can- 

 nel-coal, its colour is full-black, 

 and it does not soil the fingers. 

 It is, however, easily distinguished 

 from cannel-coal, in being specifi- 

 cally lighter than water, which 

 cannel-coal is not, and in possess- 

 ing electrical properties which can- 

 nel-coal does not. Some persons 

 have supposed that jet is a true 

 amber, differing only in the mere 

 circumstance of colour. During 

 combustion it emits a bituminous 

 smell. It is never found in strata 

 or continued masses, but always in 

 separate and unconnected heaps. 



It is formed into various trinkets, 

 and is particularly used for making 

 mourning ornaments, such as ear- 

 rings, brooches, bracelets, buttons &c. 



JEWS-STONE. 



1. An extraneous fossil, being the 

 elevated spine of a very large egg- 

 shaped sea-urchin, or echinus. 



2. A local term for basalt. In 

 Salop and Worcestershire this name 

 is applied to any hard trap-rock. 



