Opals and Onyx

Tomorrow, I am releasing the limited edition

opals and onyx collection

showstopping gemstones for every occasion

Opals and onyx are two of the most popular ever-lasting gemstones in the jewelry market.  But what are they ... really?  In a previous post on August 20, I talked about flint and chert.  Today, you will discover that opal, onyx, chert, flint, chalcedony ... they are all essentially variations on the same thing - microcrystalline grains of silica.

Onyx is a banded variety of chalcedony.  The bands are created by alternating layers of microcrystalline quartz and moganite, which is essentially quartz with a different crystal structure.  Sardonyx is a variety of onyx with bands of quartz and sard, another variety of chalcedony.  (Gemstone manufactures seem to try to make their products stand out by giving different names to essentially the same minerals).  Utah blue and orange sardonyx are examples.

Utah Sardonyx collected near Nephi, Utah

Calcite onyx is actually not onyx at all.  Calcite onyx, or cave onyx, is banded layers of calcite that form from cave formations such as stalagtites and stalagmites.  It forms much the same way, with one little layer at a time slowly precipitated.  But it is calcite instead of quartz.  Honey onyx and the most popular flowering tube onyx are examples.

Flowering Tube Onyx collected near Nephi, Utah

Cave Formations at Ruby Falls, Tennesee

Opal is the least like all the other minerals - onyx, chert, flint, and chalcedony.  It is still silica, but in opal, the silica does not form crystals of quartz.  It is a hydrated, amorphous silica "ooze".  Most often, opal is associated with volcanic activity.  Silica-rich fluids from magma flow into the surrounding rock, where the opal is precipitated in pockets and layers in the rock.  The internal structure of the silica ooze makes it refract light, which gives opals their most-sought after feature - sparkle.

There are two types of opal - common opal and precious opal.  I personally feel these names do not do them justice because "common" opal is just as amazing as precious opal.  Precious opal tends to show a play of colors and multi-color sparkle and shimmer that dances in the light.  Common opal tends to be translucent and often a single solid color, or bands of colors.

Examples of common opal include Utah bacon opal and Peruvian pink and blue opal.

Utah Bacon Opal collected near Milford, Utah

Examples of precious opal include the Honduran black matrix opal and koroit boulder opal.

Honduran Black Matrix Opal

All of these stones make beautiful cabs and stunning jewelry perfect for that special occasion or to make every day feel special.

Cabochon from Bacon Opal

Cabochon from Koroit Boulder Opal

Find the Opal and Onyx Collection at www.rubymountain5rocks.com.  Don't forget, join Club Ruby for an instant 20% discount!

Dr. Janet Bertog, owner Ruby Mountain5 Rocks