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16 March 2002

Summary of Gemstone Faceting and Crystals

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Annex to Patterning Archetypal Templates of Emergent Order: implications of diamond faceting for enlightening dialogue


Introduction

This explores typical gemstone cuts and faceting, as well as providing a tabular presentation of the relationship of many common gemstones to crystal systems and classes. The Annex also shows the common association of gemstones with the chakra system.

Technical comment

The proportions of a stone, as well as its polish and precision of faceting, determine how much of the diamond's potential fire and beauty may be released. The way a diamond is cut profoundly influence its sparkle, fire and brilliance, as well as its perceived size and even, to some degree its apparent color. In order to maximize the diamond's brilliance it must be well polished and cut in a geometrically precise manner. This means properly aligning the facets so light will enter the diamond and reflect back through the large top facet, or table of the diamond.

As a general rule only translucent, semi-translucent or clear gemstones are cut with facets. There are several basic cuts:

There are many other types of cuts of gemstones, cushion top, rose cut, pear cut, fancy cut, etc. These cuts are relatively rare compared to the six cuts described above. Bastard-cut a term used for fashioned stones which do not conform to the recognised typical forms, or which show some slight modification from the "pure" forms. The term applies only to those stones which have a regular and symmetrical arrangement of the facets; should they be irregular or haphazard the term Cap-cut is used.

There is no universal agreement on what angles to use for faceting various gemstones. Each set of faceting angles from generally accepted sources may well have slightly different optical characteristics. The definition of which is "best" is purely a matter of personal preference.

Why a diamond is cut that way?

Facets

Each facet of a brilliant has a name of its own: skew, skill, bezel, quoin, etc. facet angles [more]

Crystals and gemstones

[more; more]

Crystal
system
Crystallographic axes
Symmetry Class Examples Chakras
Number Angle Length Axes Planes Centre Subdues Opens
Cubic
Isometric
3 right angles equal 13

(6 two-fold, 4 three-fold, 3 four-fold)
9 1 element diamond   7
silicate garnet (almandine, andradite, grossular, pyrope, spessartine, uvarovite) 1 1
oxide spinel    
oxide periclase    
Tetragonal 3 right angles 2 horizontal axes of equal length; vertical axis is either longer or shorter. 5

(4 two-fold, 1 four-fold)
5 1 silicate zircon    
silicate scapolite    
Hexagonal 4 3 horizontal axes of equal length and at 60 degrees to each other. vertical axis is usually longer and at right angles to the horizontal axes. 7

(6 two-fold, 1 six-fold)
7 1 silicate beryl (emerald) 4 4
silicate beryl (aquamarine) 5 5
silicate benitoite   6
silicate sugilite   6
phosphate apatite    
oxide taaffeite    
Trigonal 4 3 horizontal axes of equal length and at 60 degree angles to each other. vertical axis is usually longer and at right angles to the horizontal axes. 4

(3 two-fold, 1 three-fold)
3 1 oxide corundum (ruby) 1 1, 2
oxide corundum (sapphire) 5 6
silicate tourmaline (buergerite, dravite, elbaite, schorl, uvite) 1 3
carbonate rhodochrosite   4
carbonate calcite   3
silicate quartz (clear) 2 7
silicate quartz (amethyst)   6
silicate quartz (rose)   4
silicate quartz (agate) 1 2
silicate quartz (citrine)  

3, 2

 

Orthorhombic 3 all at right angles to each other. all of unequal length 3

(all two-fold).
3 1 oxide chrysoberyl (alexandrite)    
silicate olivine (peridot) 3 4
carbonate sinhalite    
silicate andalusite    
silicate kornerupine    
silicate cordierite    
silicate zoisite (tanzanite)    
silicate topaz   5
Monoclinic 3 2 axes are inclined at an angle other than 90 degrees third axis is at right angles to the other two. 1

(two-fold).
1 1
silicate jade 2 4
silicate euclase    
silicate diopside    
silicate spodumene (kunzite)   4
silicate chrysocolla 2  
silicate titanite (sphene)    
carbonate azurite   5
phosphate brazilianite    
Triclinic 3 all of unequal length (least symmetrical of all crystal systems) all inclined at angles other than 90 degrees to each other. 0 0 1 silicate microcline (amazonite, perthite)   5
silicate rhodonite    
silicate kyanite   5
silicate axinite    
silicate oligoclase (sunstone)    
silicate oligoclase (moonstone) 3 6
phosphate turquoise 5 5
(Amorphous) -- -- -- -- -- -- mineraloid amber 3 2
opal 7  
tektites    

Classification of gemstones

It was only in this century that stones were classified into various categories such as precious stones, semiprecious stones and ornamental stones. In 1880, for example, the diamond, corundum, ruby, emerald, sapphire, amethyst, agate, aventurine, garnet, lapis lazuli, opal, topaz and turquoise were all classified as precious stones. Well into the 20th century the preference was to divide the minerals used in jewelry into two categories, gems (when mounted in jewelry) and ornamental stones (carvings, mosaics, inlays, etc); the term precious stone is strictly reserved for diamonds, rubies, sapphires and emeralds. Modern classification separates minerals into several categories [more]: pure elements; sulphides; halides; oxides; carbonates; phosphates; silicates; non-crystalline and organic materials

Classification of gemstones http://www.tradeshop.com/gems/classify.html

Indian classification of gems and jewels http://www.urday.com/gemo2.htm

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