Crystals are prismatic, acicular or scaly in habit; they have a perfect cleavage parallel to the brachypinacoid (M in the figure).
Sammetblende or przibramite is a variety, from Przibram in Bohemia, consisting of delicate acicular or capillary crystals arranged in radiating groups with a velvety surface and yellow colour.
It is the methyl ester of a neutral body colchicein, which may be obtained in white acicular crystals.
The difference between schists and gneisses is mainly that the latter have less highly developed foliation; they also, as a rule, are more coarse grained, and contain far more quartz and felspar, two minerals which rarely assume platy or acicular forms, and hence do not lead to the production of a fissile character in the rocks in which they are important constituents.
A sublimate may be formed of: sulphur - reddish-brown drops, cooling to a yellow to brown solid, from sulphides or mixtures; iodine - violet vapour, black sublimate, from iodides, iodic acid, or mixtures; mercury and its compounds - metallic mercury forms minute globules, mercuric sulphide is black and becomes red on rubbing, mercuric chloride fuses before subliming, mercurous chloride does not fuse, mercuric iodide gives a yellow sublimate; arsenic and its compounds - metallic arsenic gives a grey mirror, arsenious oxide forms white shining crystals, arsenic sulphides give reddish-yellow sublimates which turn yellow on cooling; antimony oxide fuses and gives a yellow acicular sublimate; lead chloride forms a white sublimate after long and intense heating.
Lehmann it melts at 168° (or at a slightly lower temperature in its water of crystallization) and on cooling forms optically isotropic crystals; at 125.6° the mass becomes doubly refracting, and from a solution rhombohedral (optically uniaxial) crystals are deposited; by further cooling acicular rhombic crystals are produced at 82.8°, and at 32.4° other rhombic forms are obtained, identical with the product obtained by crystallizing at ordinary temperatures.
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The haematoidin pigment may vary in colour from yellowish or orange-red to a ruby-red, and forms granular masses, rhombic prisms or acicular crystals.
As found in nature, saltpetre generally forms aggregates of delicate acicular crystals, and sometimes silky tufts; distinctly developed crystals are not found in nature.
It dissolves in water with evolution of heat; on evaporation a basic salt, ZrOC1 2.8H 2 0, separates out in star-shaped acicular aggregates.
Iodine dissolves in an aqueous solution of the salt to form a dark brown liquid, which on evaporation over sulphuric acid gives black acicular crystals of the tri-iodide, K1 3.
Elongated, cylindrical, rounded at both ends; thick cuticle with acicular spicules; radula polystichous or wanting.
In Pinus the only leaves produced on the main stern and the lateral shoots are scales, the acicular leaves of the tree growing from axillary shoots.
The monoxychloride, WOC14, is obtained as red acicular crystals by heating the oxide or dioxychloride in a current of the vapour of the hexachloride, or from the trioxide and phosphorus pentachloride.
Tungsten disulphide, W52, is obtained as soft black acicular crystals by the action of sulphur, sulphuretted hydrogen or carbon bisulphide on tungsten.
Quinine of commerce is the neutral sulphate,C20H24N202 H2S04.8H20, which occurs in commerce in the form of very light slender white acicular crystals.
It crystallizes in white or pale fawn-coloured acicular prisms or silky needles, and is soluble in alcohol and ether, and in loo parts of cold and 3 of boiling water; it is without odour and has an astringent and an acid taste and reaction.
Sometimes the same plant produces both kinds of leaves on different branches, or the young plants produce acicular leaves, while those of the older plants are squamiform.
Crystals of arsenic belong to the rhombohedral system, and have a perfect cleavage parallel to the basal plane; natural crystals are, however, of rare occurrence, and are usually acicular in habit.
Distinctly developed crystals are, however, of rare occurrence; they are usually acicular with acute pyramid-planes and are repeatedly twinned on the prism.
These are, according to Meyer, acicular crystals, which he calls tricizites.