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Encyclopedia Britannica - Main :: HIG-HOR |
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HORNBLENDE , an important member of the amphibole group of rock-forming minerals. The name is an old one of German origin, and was used for any dark-coloured prismatic crystals from which metals could not be extracted. It is now applied to the dark-coloured aluminous members of the mono-clinic amphiboles, occupying in this group the same position that augite occupies in the pyroxene group. The monoclinic crystals are prismatic in habit with a six-sided cross-section; the angle between the prism-faces (M), parallel to which there are perfect cleavages, is 55 49'. The colour (green, brown or black) and the specific gravity (3.0-3.3) vary with the amount of iron present. The pleochroism is always strong, and the angle of optical extinction on the plane of symmetry (x in the figure) varies from o to 37. The chemical composition is expressed by mixtures in varying proportions of the molecules Ca(Mg,Fe)s(SiO3)s, (Mg,Fe)(Al,Fe)2SiO6 and NaAl(SiO )s. Numerous varieties have been distinguished by special
York
Hornblende occurs as an essential constituent of many kinds Buffon, as was his manner, enlarges on the cruel injustice done to these birds by Nature in encumbering them with this deformity, which he declares must hinder them from getting their food with ease. The only corroboration his perverted view receives is afforded by the observed fact that hornbills, in captivity at any rate, never have any fat about them. 2In The Malay Archipelago (i. 213), Wallace describes'a nestling hornbill (B. bicornis) which he obtained as " a most curious object, as large as a pigeon, but without a particle of plumage on any part of it. It was exceedingly plump and soft, and with a semi-transparent skin, so that it looked more like a bag of jelly, with head and feet stuck on, than like a real bird.' of igneous rocks, such as hornblende-granite, syenite
mineral
Vesuvius
York
HORN-BOOK, a name originally applied to a sheet containing the letters of the alphabet, which formed a primer for the use of children. It was mounted on wood
paper , contained first a large crossthe criss-crossefrom which the horn-book was called the Christ Cross Row, or criss-cross-row. The alphabet in large and small letters followed. The vowels then formed a line, and their combinations with the consonants were given in a tabular form. The usual exorcism" in the name of the Father and of the Sonne and of the Holy Ghost, Amen "followed, then the Lord's Prayer, the whole concluding with the Roman numerals. The horn-book is mentioned in Shakespeare's Love's Labour's Lost, v. 1, where the ba, the a, e, i, o, u, and the horn, are alluded to by Moth. It is also described by Ben Jonson" The letters may be read, through the horn, That make the story perfect." End of Article: HORNBLENDE If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/HIG_HOR/HORNBLENDE.html"> HORNBLENDE </a> |
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