Crystals of azurite belong to the monoclinic system; they have a vitreous lustre and are translucent.
The crystals of prismatic habit represented in figs.
These are, according to Meyer, acicular crystals, which he calls tricizites.
Albumen crystals are also to be found in the cytoplasm, in leucoplasts and rarely in the nucleus.
As crystals, and as stalactitic, encrusting, reniform, massive, earthy and occasionally pulverulent forms as "sulphur meal."
Crystals of sulphur are transparent or translucent and highly refractive with strong birefringence; they have a resinous or slightly adamantine lustre, and present the characteristic sulphur-yellow colour.
Cesena and Perticara are well-known localities in this district, the latter yielding crystals coated with asphalt.
Fine crystals occur at Conil near Cadiz; whilst in the province of Teruel in Aragon, sulphur in a compact form replaces fresh-water shells and plant-remains, suggesting its origin from sulphur-springs.
The solution obtained may be evaporated in vacuo until it attains a density of 1.46 when, if partially saturated with potassium hydroxide and filtered, it yields crystals of potassium pentathionate, K 2 S 5 0 6.3H 2 0.
It forms monoclinic crystals which are very soluble in water.
Boron dissolves in molten aluminium, and on cooling, transparent, almost colourless crystals are obtained, possessing a lustre, hardness and refractivity near that of the diamond.
Crystals have the form of small, sharply defined cubes of an oliveor grass-green colour, and occur together in considerable numbers on the matrix of the specimens.
Of the suspended substances, grains of caoutchouc, drops of resin and oil, proteid crystals and starch grains may be mentioned.
In the red variety of Cucurbita pepo these crystals may consist of rods, thin plates, flat ribbons or spirals.
Many of the hollow agates of Brazil and Uruguay contain a crop of amethyst-crystals in the interior.
Free sulphur may also result from the decomposition of pyrites, as in pyritic shales and lignites, or from the alteration of galena: thus crystals of sulphur occur, with anglesite, in cavities in galena at Monteponi near Iglesias in Sardinia; whilst the pyrites of Rio Tinto in Spain sometimes yield sulphur on weathering.
Beautiful rock crystals occur in veins in the corries.
The most important subjects of his inquiries are enumerated by Forbes under the following five heads: - (1) The laws of polarization by reflection and refraction, and other quantitative laws of phenomena; (2) The discovery of the polarizing structure induced by heat and pressure; (3) The discovery of crystals with two axes of double refraction, and many of the laws of their phenomena, including the connexion of optical structure and crystalline forms; (4) The laws of metallic reflection; (5) Experiments on the absorption of light.
In this line of investigation the prime importance belongs to the discovery (1) of the connexion between the refractive index and the polarizing angle, (2) of biaxial crystals, and (3) of the production of double refraction by irregular heating.
Crystals of barytes are orthorhombic and isomorphous with the strontium and lead sulphates (celestite and anglesite); they are usually very perfectly developed and present great variety of form.
Crystals of barytes may be transparent and colourless, or white and opaque, or of a yellow, brown, bluish or greenish colour.
Well developed crystals are extremely common, but the mineral occurs also in a granular, earthy, or stalactitic condition.
Barytes is of common occurrence in metalliferous veins, especially those which yield ores of lead and silver; some of the largest and most perfect crystals of colourless barytes were obtained from the lead mines near Dufton in Westmorland.
It is found also in beds of iron ore, and the haematite mines of the Cleator Moor district in west Cumberland have yielded many extremely fine crystals, specimens of which may be seen in all mineral collections.
In the neighbourhood of Nottingham, and other places in the Midlands, barytes forms a cementing material in the Triassic sandstones; amber-coloured crystals of the same mineral are found in the fuller's earth at Nutfield in Surrey; and the septarian nodules in London Clay contain crystals of barytes as well as of calcite.
Crystals are found as a rarity in the amygdaloidal cavities of igneous rocks.
Artificially prepared crystals of barytes may be obtained by allowing a solution of a soluble barium salt to diffuse slowly into a solution of a soluble sulphate.
Crystals of a different form are deposited from a strong boiling solution of the acid.
It forms very hard metallic-looking crystals, burns in oxygen and is not attacked by acids.
It forms silky crystals which melt at 6° C., and boil at about 144° C. with decomposition.
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.
- On the theory that crystal form and structure are the result of the equilibrium between the atoms and molecules composing the crystals, it is probable, a priori, that the same substance may possess different equilibrium configurations of sufficient stability, under favourable conditions, to form different crystal structures.
In the article Crystallography the nature and behaviour of twinned crystals receives full treatment; here it is sufficient to say that when the planes and axes of twinning are planes and axes of symmetry, a twin would exhibit higher symmetry (but remain in the same crystal system) than the primary crystal; and, also, if a crystal approximates in its axial constants to 'a higher system, mimetic twinning would increase the approximation, and the crystal would be pseudo-symmetric.
The sun knows that you like to see the world covered with beautiful white snow and so he kept back all his brightness, and let the little crystals form in the sky.
White Pond and Walden are great crystals on the surface of the earth, Lakes of Light.
Gabriel took the crystals with a nod.
Light snow had begun to fall—tiny crystals hardly visible in the light of the lamp across the street.
Mountain winters were always a surprise to lowlanders and easterners, where the chemistry of moisture played games that produced slush and wet snow, not the sparkling crystals so soft a broom could clear a foot-deep snowfall with a few swishes.
With deadly accuracy, she threw the ball at him, laughing when it bounced off his leather coat and sprayed a mist of white crystals in his face.
They form yellow or bronze-coloured crystals, which decompose on boiling their aqueous solution.
Natural crystals are sometimes honey-yellow to brown in colour, but this appears to be due to alteration.
Pharmacosiderite is a mineral of secondary origin, the crystals occurring attached to gozzany quartz in the upper part of veins of copper ore.
They are composed of a homogeneous proteid substance, and often contain albuminoid or proteid crystals of the same kind as those which form the pyrenoid.
Such crystals occur either in cavities in mineral-veins and in granitic rocks, or as a lining in agate geodes.
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 decomposed by water, and with a solution of yellow phosphorus in carbon bisulphide it gives a red powder of composition PBI 2, which sublimes in vacuo at 210° C. to red crystals, and when heated in a current of hydrogen loses its iodine and leaves a residue of boron phosphide PB.
It forms slightly coloured small crystals possessing a strong disagreeable smell, and is rapidly decomposed by water with the formation of boric acid and sulphuretted hydrogen.
Crystals are prismatic, acicular or scaly in habit; they have a perfect cleavage parallel to the brachypinacoid (M in the figure).
Cadmium sulphate, CdSO 4, is known in several hydrated forms; being deposited, on spontaneous evaporation of a concentrated aqueous solution, in the form of large monosymmetric crystals of composition 3CdSO 4.8H 2 O, whilst a boiling saturated solution, to which concentrated sulphuric acid has been added, deposits crystals of composition CdSO 4 4H 2 0.
Crystals were first found in Cornwall (at Wheal Jane, near Truro, associated with pyrrhotite) by J.
Each cell contains a zinc plate, immersed in a solution of zinc sulphate, and also a porous chamber containing crystals of copper sulphate and a copper plate.
It forms dark red crystals isomorphous with ferrous sulphate, and readily soluble in water.
It separates in the form of small rose-red crystals, which decompose on boiling with water.
The crystals are feebly doubly refracting, and in polarized light exhibit a banded structure parallel to the cube faces.
