H O R 



H Y A 



ness, and the results of fusion. Its pow- 

 der is not soft to the touch like that of 

 asbestus. Cleaveland. 

 HO'RNBLENDE SCHIST. One of the me- 

 tamorphic rocks, composed principally 

 of hornblende, with an uncertain pro- 

 portion of felspar, and sometimes grains 

 of quartz : its colour is usually black, 

 Dr. M'Culloch observes, " hornblende 

 schist may at first have been mere clay, 

 for clay or shale is found changed by trap 

 into Lydian stone, a substance differing 

 from hornblende schist almost solely in 

 its compactness and in the uniformity of 

 its texture. Argillaceous schist, when in 

 contact with granite, is sometimes con- 

 verted into hornblende schist, the schist 

 becoming first siliceous, and, at the con- 

 tact, hornblende schist." 

 HORNBLE'NDIC. Containing hornblende ; 

 resembling hornblende. A mass of chi- 

 astolitic and hornblendic slates forms the 

 base of the clay-slate system of Cumber- 

 land. 



HO'RNSTONE. A siliceous mineral ; a sub- 

 species of quartz. It has usually a dull 

 and splintery fracture, but sometimes it 

 is conchoidal. It differs from felspar in 

 being infusible without the addition of 

 an alkali. It occurs massive, and in ex- 

 traneous external shapes ; lustre dull or 

 glimmering, opaque or translucent on the 

 edges ; sometimes the whole mass, if 

 thin, has the strong translucency of cer- 

 tain horns. According to Kirwan, its 

 constituents are, silica 72, alumina 22, 

 carbonate of lime 6. Its colours are nu- 

 merous, and commonly dull. Its infusi- 

 bility by the blow-pipe distinguishes it 

 from petrosilex and jade. Its translu- 

 cency serves to render it distinct from 

 jasper. It is generally more dull than 

 flint, and emits sparks more feebly with 

 steel. It is deficient in lustre in com- 

 parison with quartz. 



Professor Cleaveland observes, " so 

 much ambiguity of meaning is attached 

 to the word hornstone, that it would be 

 favourable to the interests of mineralogy 

 if this term could be banished from its 

 nomenclature. It has by some been 

 confounded with hornblende : by others 

 it has been applied to two minerals en- 

 tirely distinct. This confusion and ob- 

 scurity in the use of the word hornstone, 

 appear to have arisen in part from acci- 

 dental circumstances. It is asserted by 

 Kirwan, on the authority of Henckel, 

 that this word was originally employed 

 by miners to designate a certain stone, 

 which they found difficult to be cul 

 through in consequence of its tenacity 

 But a certain degree of translucency is 

 also a character of horn. Hence, as 

 mineralogists did not observe both these 



properties to unite in the same mineral, 

 they subsequently applied the term horn- 

 stone, to two distinct minerals, one of 

 which possessed tenacity only, while 

 the other was translucent, but not re- 

 markably tenacious. Hence the applica- 

 tion of the term hornstone to the mineral 

 now called hornblende." 

 HO'RNSTONE PORPHYRY. The Hornstein 

 porphir of Werner. A variety of por- 

 phyry of a red, brown, purple, or black- 

 ish colour. Fracture splintery and con- 

 choidal. Emits sparks when struck with 

 steel. Is susceptible of a fine polish. 

 HO'RTUS siccus. (Lat.) A collection of 



dried plants. 

 HU'MBOLDITE. A rare mineral, thus named 



after Humboldt. 



HU'MERAL. (from humerus, Lat.) Be- 

 longing to the shoulder. 

 HU'MERUS. (Lat.) The shoulder. 

 HU'MID. (humidus, Lat. humide, r.umido, 



It.) Moist ; wet ; damp ; watery. 

 HUMI'DITY. (humidite, Fr. umidita, It.) 



Moisture ; dampness. 



HU'MITE. A reddish-brown mineral, found 

 at Somma, thus named after Sir A. 

 Hume. 



HU'MMOCK. A mound of land. 

 HY'ACINTH. (vdicivQoQ, Gr. hyacinthus, 

 Lat. hyacinthe, Fr.) The Hiazinth of 

 Werner ; Zircon hyacinthe of Brong- 

 niart. A mineral ; a variety of pyrami- 

 dal zircon, of a hyacinth-red colour. It 

 is crystallized, and when in distinct cry- 

 stals its ordinary form is a four-sided 

 prism, terminated by four rhombic planes. 

 Each plane angle at the summit is 73 

 44'. It is found in beds of streams and 

 rivers along with rubies, sapphires, &c., 

 but sometimes it occurs in the primary 

 rocks. It consists of, zirconia 70, silica 

 25, oxide of iron 0'5. It is considered a 

 gem, but is little used as such. Before 

 the blow-pipe it loses its colour, but re- 

 tains its transparency. With borax it 

 melts into a transparent glass. 

 HYACI'NTHINE. A mineral of a brown or 

 greenish colour, usually crystallized in 

 rectangular eight-sided prisms. Frac- 

 ture imperfectly conchoidal. Transparent. 

 Causes double refraction. 

 HYACI'NTHINE. Of the colour of hya- 

 cinth ; resembling hyacinth ; containing 

 hyacinth. 



HYALVE'A. (So named from its semi- 

 transparent shell.) A genus of Ptero- 

 pods, or animals furnished with organs 

 only for swimming and sailing. The 

 Hyalcsa has the appearance of a bivalve 

 with soldered valves, the upper one being 

 the largest ; this difference of size of the 

 seeming valves causes an aperture through 

 which the animal sends forth two large 

 yellow and violet wings, or sails, rounded 



