Fracture, conchoidal

Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands 3.1 percent on solidifying therefore, it should not be stored in glass or metal containers, because they may break as the metal solidifies. 

Obsidian Making tools and decorative objects Natural glass Extremely dense sharp edges conchoidal fracture... 

Flint Making tools Mainly silica Very compact sharp edges, conchoidal fracture... 

Rock crystal Vitreous Transparent Colorless Conchoidal fracture... 

The fracture patterns of noncrystalline or partly crystalline, partly amorphous materials are unpredictable. Conchoidal fracture is typical of glass and yields odd-shaped flakes of various sizes. 

The common gray, brown, or black flint result from admixed iron oxides or organic compounds. Pure quartz is usually colorless and transparent. The conchoidal fracture typical of flint was a boon to primitive humans, who desired clean, smooth, sharp edges that were not susceptible to uniform wear. This physical attribute and the densities of flint reflect the patterns of aggregation of its fibrous constituents. 

FIGURE 19 Flint tools. Axes, scrapers, and knives. Flint is a hydrated form of ciyp-tociystalline silica that occurs naturally as irregular nodules in chalk deposits. It is colorless and translucent when pure, but opaque and often colored when it contains impurities. When struck, flint breaks with a conchoidal fracture and the fragments formed have smooth, sharp edges. It is for this reason that prehistoric humans used flint to make tools. Since it also sparks when struck, flint was also used, until the eighteenth century, for lighting Are. 

Klaproth mentioned two kinds of pitchblende, the first of which was a brownish black, opaque, brittle, massive, resplendent kind with a conchoidal fracture, found in the mines or galleries at Joachimsthal, Saxon Edelleutstolln, and Hohe Tanne. 

The kukersites mined from the Estonia deposit have a light chocolate-brown colour in dry condition (10YR 6/4, i.e., light yellowish brown Munsell Color Company 1994), with a conchoidal fracture oblique to the lamination. The density is less than 2.1 g/cm3, but varies depending on the content of clastic material and carbonate minerals versus organic matter. 

After the kneading has been completed the mass is pressed to form press cakes which are then dried. These cakes are hard and give a conchoidal fracture. Pressing is done either (a) in the same edge runners (b) in hydraulic presses. 

Figures 3-5 are SEM photographs of each glass composite at 2000-fold magnification. These photographs show conchoidal fracturing indicative of glass, as well as some very fine particles attached to the larger particles.

Good charcoal is very dark, possesses a bright lustre and somewhat conchoidal fracture it resists gradual pressure to a considerable extent, and produces a sharp sonorous sound when allowed to fell upon a hard body. It should burn when ignited without either flame or smoke, and when handled no stain ought to remain. Although in bulk it floats in water,... 

Air-dried lignite, conchoids fracture, with twenty per cent, moisture and no ash,. end ton per cent, ash,... 

Amorphous Selenium.—(1) Vitreous Selenium.—When molten selenium is cooled in not too protracted a manner, no definite solidification or crystallisation ensues, but the mass gradually hardens and the product really represents a strongly undercooled liquid like glass. Vitreous selenium is a brittle reddish-brown substance, exhibiting a conchoidal fracture. When finely powdered and viewed in thin layers it has a deep red colour. This form has an average density of 4-28 5 the value varies slightly, possibly owing to the presence of other allotropic modifications of the element. 

Broken surfaces have a brilliant, glassy luster and are jet-black in color with a perfect conchoidal fracture. Remnants of the precataclasis bounding surface of each nodule retain a dull luster owing to a closely pitted, etched surface. Maximum size of the composite nodule ranges up to 5 cm. but can be as little as 0.5 cm. 

Vitrain. Occurs in uniform bands up to xh inch in thickness. The bands are a brilliant black, having the luster of broken glass, and complete homogeneity. Breakage into cube-like pieces and pieces with conchoidal fractures are common. 

It occurs in irregular masses showing a conchoidal fracture. Hardness, 2,25 sp gr, 1.09 luster, resinous color, yellow to reddish or brownish it may be cloudy. Some varieties will exhibit fluorescence. Amber is transparent to translucent, melts between 250 and 300°C. 

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