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Geology

Geological processes and formations.

abandoned mine [1024×683] - Imgur Russia

E107 Introduction to Gemstones This poster begins by showing the most popular gemstones, grouped together by class. It explains the important "Four C’s" of gemstones - Cut, Clarity, Color and Caret, followed by an introduction to other important qualities, such as Asterism, Opalescence, Hardness and Pattern. The next row provides wonderful illustrations of the important gemstone cuts, accompanied by an explanation. This is followed by an introduction to cabachons. It then presents an as

The diagram below and opposite shows gemstone cuts from antiquity to the present. True 'artists in stone', lapidary has evolved over thousands of years. During antiquity, cabochons were initially the only cutting style available. Guided by the natural facets of the gemstone's crystal structure, the lapidary cut gems in increasingly more complex ways over time. The earliest of these involved removing the tops of crystals. In the last hundred years, technological advances have allowed cutters to d

  • Emy Magpie

    [...] develop some breathtaking innovations. New cuts such as the Wobito Snowflake™ would have been difficult, if not impossible, to create just 200 years ago. The general perception is that faceting lower quality rough is not economically viable. When I first started in the gem business, I assumed only lower quality rough was cut 'en cabochon', but this is not the case. Individual preferences vary and today, fine quality gems are cut in both styles. Please don't make quality assumptions based solely on whether a gem has been faceted or not.

The round brilliant cut possesses the angles and proportions once thought necessary to display a Diamond's best dispersion (fiery flashes of colour), scintillation (play of light) and its characteristic brilliance (white light reflections). While also used for other gemstones, the brilliant cut was developed specifically for Diamonds. The standard number of facets in a round brilliant cut is 57 (or 58 if you include the culet).

  • Emy Magpie

    The brilliant cut was developed by several people, including Vincenzio Perruzzi (an 18th-century Venetian cutter), Henry Morse (he opened America's first Diamond cutting workshop in Boston, Massachusetts in 1860) and the Russian mathematical genius Marcel Tolkowsky (a member of a large and powerful Diamond family, he calculated the cuts necessary to create the ideal round brilliant cut in his book, 'Diamond Design' published in 1919).

Classic gemstone shapes and cuts

Plate 1: Brilliant Forms. 1 a, b, c, Double-cut. 2 a, b, c, English double-cut (double-cut brilliant with star). 3 a, b, c, Triple-cut, old form. 4 a, b, c, Triple-cut, new form round. 5 b, c, The same oval. 6 b, c, The same, pear-shaped. 7 a, b, c, The same triangular. 8 a, Half-brilliant.

Plate 3: 1-8 Rosetts (Rose-cut). 1 b, Rose, round. 2 b, Rose, pear-shaped. 3 a, Dutch Rose. 4 a, Brabant Rose. 5a, 6 a, Roses of other forms. 7 a, b, Rose recoupeée. 8 a, b, Cross-rose. 9 a, Double rosette (pendeloque). 10 Briolette. 11 a, b, Table-stone. 12 a, 13 b, Thin-stone. 14 a, b, Table-stone, with brilliant form above. 15 a, b, 16 b, Thick-stone. 17 b, Cabochon, simple (hollowed). 18 b, The same with facets. 19 b, Double Cabochon.

Plate 2: Star and step cuts: 1a, b, c, Star-cut (of Mr. Cair). 2, a, b, Step-cut, four-sided. 3 b, Step-cut, six-sided. 4 b, c, Step-cut, eight-sided. 5 a, b, Mixed-cut. 6 a, b, Cut with double facets. 7 a, b, c, Cut with elongated brilliant facets. 8 a, b, c, Maltese cross cut.

river under vatnajökull glacier, iceland, Spacescape!!

Isle of Skye, Scotland.

Landscape strata

For all my geology friends.

whats hot geology

BBC News - Undersea mountains march into the abyss - via bit.ly/epinner [BBC Video]

BBC News - Rise and fall of underwater volcano revealed - via bit.ly/epinner