Varieties of Chalcedony


Since quartz is the most abundant mineral in the earth's crust and the minutely crystalline chalcedonic form is found in every country, it is not surprising that there are a large number
of distinct varieties. Although hobbyist rock and mineral collectors distinguish literally hundreds of varieties of chalcedony, those described below are the only ones of significance to the jeweler.

  1. Chalcedony

    In general usage, the terms chalcedony and cryptocrystalline quartz are synonymous; therefore, chalcedony may be applied correctly to any of the numerous varieties of this large mineral family. However, it is also sometimes used as a specific variety name to refer to the semi-transparent to translucent white to pale grayish-blue material.

  2. Chalcedony "Moonstone "

    This variety is semitransparent white to gray (milky) chalcedony that only vaguely resembles moonstone. It lacks the floating light effect that is characteristic of true adularescence in genuine moonstone. Buy moonstone necklaces

  3. Chrysoprase

    Semitransparent to translucent light to medium yellowish-green chalcedony is called chrysoprase. This term should be reserved for the natural material; it should not be applied to the dyed dark green chalcedonic quartz that is often sold as either "green onyx" or "chrysoprase"

  4. Carnelian

    Semitransparent to translucent red, orange-red to brownish-red or brownish-orange chalcedony is called carnelian. These colors may also be produced by heat treating nearly colorless chalcedony. Buy carnelian necklaces

  5. Sard

    Sard is similar to carnelian, except that its color is usually less intense; i.e., more brownish and somewhat darker. It tends more to the dark-reddish colors and carnelian to the lighter, predominantly orange hues. Unfortunately, there is no distinct dividing line between sard and carnelian.

  6. Bloodstone or Heliotrope

    Semi translucent to opaque dark-green chalcedony with red to brownish-red spots is called either bloodstone or heliotrope. It is often used for men's rings, either as flat tablets or in carved forms. Buy Bloodstone necklaces

  7. Prase

    The term prase is applied to translucent light-grayish yellow-green chalcedony. It finds little application in the jewelry trade.

  8. Agate

    The term agate is applied correctly to chalcedony in which the color is distributed in curved bands or layers. The banded appearance is distinguished by a difference in either color or translucency, or both, between adjoining layers of chalcedony. The word agate is often used somewhat loosely with a prefix to describe material that is not banded; e.g. landscape agate (containing inclusions resembling a landscape), fortification agate (composed of straight, intersecting bands), and moss agate or mocha stone (milky-white chalcedony with green, black or brown inclusions distributed in dendritic patterns).
    Because of its rather porous nature, gray and white agate is particularly susceptible to dyes of various colors. The dye may color the material unequally, preserving the banded appearance, or it may penetrate porous materials so evenly that a single color results. Buy agate necklaces

  9. Onyx

    The only proper use of the term onyx is to describe chalcedony composed of straight, parallel bands. It is used incorrectly when applied to grayish chalcedony or agate that has been dyed to produce the solid-colored material known e s "black onyx", "green onyx", etc. These misnomers have been used for this purpose for so long and so consistently that many jewelers do not realize that they are incorrect and misleading. If the onyx exhibits
    bands of sard colors alternating with either white or black parallel bands, it is known as sardonyx. Cornelian onyx has alternate parallel bands of carnelian colors with either black or white.
    White banding is much more common than black; in fact, natural black chalcedony is not too frequently encountered. A cross-section of chalcedony showing both curved bands (agate) and straight, parallel bands (onyx).

  10. Jasper

    The name jasper is applied to most of the semi translucent to opaque chalcedonies that occur throughout the word in a wide variety of colors, often without a pattern of any kind. It may be red, yellow, brown, green, grayish blue or any combination thereof. It is frequently dyed blue and sold as "Swiss lapis" or "German lapis".

  11. Plasma

    Semi translucent to almost opaque dark-green chalcedony with white or yellowish spots is called plasma. It is essentially bloodstone but lacks the red spots. Both plasma and prase are sometimes used as inexpensive jade substitutes.

  12. Chrysocolla Chalcedony

    Translucent to semi-translucent intense light-blue or blue-green chalcedony, the color of which is caused by minutely distributed chrysocolla (a copper silicate), is one of the loveliest varieties of chalcedony. In its finest quality it rivals the most beautiful turquoise in appearance. Unfortunately, however, it is quite rare.

  13. Agatized Wood

    Wood that has been replaced entirely by chalcedony resembles a patterned jasper, and is a rather attractive material for ornamental purposes. Almost all chalcedonic colors are represented, including red, yellow, black and brown. It is also called silicified or petrified wood.



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