by Rose Marion, Wire-Sculpture.com

Moss Agate and Plume Agate, one in a Series on Quartz

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Just as there are many kinds of included quartz, there are several varieties of included agate. Sagenite agate, or sagenitic agate, has needlelike inclusions in a sunburst or fan shape, and come in a variety of colors. Here’s an example of a neon yellow sagenitic agate! Dendritic agate, such as Montana agate, just like its quartz counterpart, has thin, dark, tree or branchlike inclusions. Plume agate has featherlike inclusions that resemble smoke, clouds, or feathers. Finally, moss agate has the appearance of green moss, seaweed, or blue cheese on a translucent background. Moss agate is the most common and most well-known included agate for jewelry makers.

Some rockhounds don’t consider these included agate stones to be true agate because they do not have the concentric  typical of most agates banding (banding formed in gradually larger circles that share a center point). However, they are definitely part of the quartz-chalcedony-agate family of silica minerals, formed from silicone dioxide. In fact, Montana agate and Plume agate are among the top tier of agates in jewelry making, surpassed only by rare stones such as fire agate.

Moss Agate

Moss agate is typically a green agate with pale to translucent patches of stone; tree agate shares the green, moss-like inclusions but has white opaque patches, rather than translucence.

Montana moss agate is unique in that it originally formed in the volcanic region of Yellowstone National Park. Now it can be found in the gravel of the Yellowstone River in Montana, and typically has red (iron oxide) and black (manganese oxide) large inclusions on a translucent background.

Plume Agate

Plume agate draws its name from the fluffy, feather-like shapes it exhibits. There are several types of plume agate, including Priday, Graveyard Point, Del Norte, West Texas, and Mexican Plume. This plume agate is from Texas; I have a cab of Texas plume agate that shares the same gold, orange, green, and white colors.

In Tucson, I saw Graveyard Point Plume Agate for the first time: this distinctive golden, tan, white, and gray-blue (and sometimes pink) agate is named for the stone’s location, found in the Owyhee Mountains along the Idaho-Oregon border, near the burial place of an 18th century massacre.

Priday plume agate is another name you may come across, which was a rare plume agate found on the Priday ranch outside Madras, Oregon, round in thunder eggs. However, this agate is practically played out. You can find pictures of beautiful Priday Plume agate stones here.

The Regency Rose variety of plume agate is located near the Graveyard Point area and has the tan hues of that stone as well as reds and pinks.

Next week, I will cover some agate you may have wire wrapped, or seen in person: thundereggs, geodes, and I’ll also touch on crazy lace agate. Have you made wire jewelry with thunderegg agate, geodes, or crazy lace agate? Send your agate pictures to tips@wire-sculpture.com, and they could be featured!

Resources

• Dandy Slab Saginitic Agate
• Agate with Inclusions
• Minerals N More Graveyard Point Plume Agate
• Wikipedia Moss Agate
• AZ Blue Rockers Priday Agate

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by Rose Marion, Wire-Sculpture.com

Fire Agate and Iris Agate, one in a Series on Quartz

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Fire Agate

Fire agate is a special kind of agate that appears brown from a distance. However, upon closer inspection, this agate is botryoidal in appearance (as I mentioned last week, that means it looks like a boiling pan of water caught bubbling, frozen in time – or like a bunch of grapes). What makes fire agate more interesting than typical botryoidal agate is its color play. Upon its brown background, a rainbow fire plays, with iridescent red, green, gold, and sometimes blue lighting up the surface of the stone.  Fire agate received its name from the feeling of staring into the embers of a fire, resulting in a similar color play.

How did fire agate acquire its firey colors? It is thought that hot water, filled with colloidal silica and iron oxide and heated by volcanoes, raced into cavities in rock and then slowly cooled, forming a hard agate. Alternating layers of silica and iron oxide, forming over time, cause the schiller and iridescence. Fire agate is especially rare because unlike regular quartz, which is found all over the world, fire agate is only found in pockets of the southwestern US and northern Mexico. It’s estimated that fire agates are 24-36 million years old, due to the timing of volcanic activity in that region of the world.

There are 3 factors that contribute to fire agate’s rarity and high cost to be used as a gem in jewelry: as I mentioned, it has a unique creation, and is only found in specific locations. The third factor is lapidary effort. The botryoidal agate must be carefully shaped, removing the outermost layer to perfectly reveal the best colors. Removing too much chalcedony from the top layer will ruin the iridescent effect, and too little will leave the surface dull. This is why, when you visit Tucson or other gem shows and see fire agate cabochons resting in a tub of water or polished in a case, most are not calibrated-cut, but freeform.

Despite the delicate process of finishing a fire agate stone, the stones themselves are very sturdy and durable. Although it has a strong resemblance to opal, fire agate does not share the danger of cracking or crazing. The layers will not flake off, nor will the stone lose its shine: like its quartz and agate siblings, fire agate has a Mohs hardness of 6.5-7, much tougher to scratch than window glass.

For an amazing gallery of fire agate pictures, click here!

Metaphysically speaking, Fire Agate is said to have a deep, calming energy bringing security and safety. It is also linked to the fire element, of course, bringing vigor and opening the root chakra. it is also said to aid in conquering addictions and harmful desires.

Crackle Fire Agate

There is another type of stone that is often called fire agate by vendors, which we call crackle fire agate. This “stone” is typically either glass or carnelian that has been heat treated to produce the lava-like lines in the stone. While also in demand, crackle fire agate is not its rare and pricey cousin, real fire agate. The crackle fire agate on Wire-Sculpture is real agate that has been dyed and heat treated to achieve the firey, crackle effect.

Iris Agate

Iris agate is another, lesser-known kind of iridescent agate. Iris agate is also called rainbow agate, although some vendors simply call any agate that is colorful, “rainbow agate,” even when it does not have the iridescent effect. When true iris agate is thinly sliced, it shows all the colors of the rainbow! The effect is more delicate than fire agate. This rainbow effect is the result of very tightly packed, very thin layers and banding, and can occur in colorless or pale chalcedony. It is also mostly found in North America, although some has been recorded in Argentina. Because it must be sliced so thinly, iris agate is fairly rare in jewelry. You can read a complete analysis of iris agate at this link.

Next week, I will cover some agate you have probably wire wrapped, or seen in person: moss agate and plume agate. Have you made wire jewelry with moss agate or plume agate (including Graveyard Point Plume Agate)? Send your agate pictures to tips@wire-sculpture.com, and they could be featured!

Resources

• AgateLady’s Iris Agate
• Crystal-Cure.com
• Mindat.org Fire Agate
• Mindat.org Iris Agate
• Minoscam.org Iris Agate
• Wirewrapjeweler.com Fire Agate

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by Rose Marion, Wire-Sculpture.com

Orbicular Agate, one in a Series on Quartz

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In today’s agate article we will discover orbicular agate, bloodstone, and botryoidal agate. I apologize for the lack of pictures; these are some rare forms of agate. Instead, I have included several links so you can visit several rockhounds’ private collections of these unique agates. Please enjoy!

Bloodstone is often categorized with jasper because of its opacity, but it is actually more like a moss agate (which will be covered in a future article) with green and hematite specks. Bloodstone can also be more translucent, which is when it is categorized with agate. As Dale mentioned in her article on Bloodstone, "the type of bloodstone that is considered to be a gem-"stone" is a high-quality, translucent, rich green with many well distributed bright red splashes."

Orbicular Agate: As shown with bloodstone, the components that make up rocks and gems have quite a bit of overlap between agate and jasper, including the orbicular varieties. As you may remember from Dale’s jasper discussion, the kinds of jasper that have circles or spherical inclusions – "needle-like crystals of different minerals in a radial structure" – are called orbicular jasper, such as ocean jasper and Dalmatian jasper. However, that is practically a synonym of orbicular agate. But – what are the types of round-spotted agate?

Polka dot agate has round spots on a translucent background in a variety of colors, such as blue, brown, yellow, gray, and green, as you can see in this example. It can be found in several locations, Oregon being one of the well-known US locations, yielding slabs like these.

Pigeon blood agate is named for its bright red hue from the high iron content of the stone; pigeon blood agate is often clear with a few bright red spots, while others have many red inclusions and a translucent background. This agate is found in Utah. You can understand the bloody connection by taking a peek at this pigeon blood agate and the cabochons on this page.

A little different from orbicular agate is botryoidal agate, also called grape agate. "Botryoidal" comes from the Greek term for a "bunch of grapes." This type of agate really does look like a bunch of grapes: spheres form in the layers, rather than flat or banded layers. These bubble-like structures can be on the surface, which looks like a pot of boiling water frozen in time. Click here to see some colorful examples of botryoidal agate. The grape- or bubble-like structures can also form away from the surface, into the stone, called turtlebacking: here is an example of a turtleback blue agate cabochon. What an interesting effect! This adds a deep dimension to the cabochons. Several other minerals can present in a botryoidal or globular shape, including fluorite, hematite, and malachite.

What causes the botryoidal feature? From its Wikipedia entry, "Each sphere (grape) in a botryoidal mineral is smaller than that of a reniform mineral, and much smaller than that of a mamillary mineral. Botryoidal minerals form when many nearby nuclei, specks of sand, dust, or other particles, are present. Layers of mineral material are deposited radially around the nuclei. As more material is deposited, the spheres grow larger and eventually overlap with those that are nearby. These nearby spheres are then fused together to form the botryoidal cluster."

Next week’s article will cover fire agate and iris agate – I can’t wait! Have you made wire jewelry with fire agate or iris agate? Send your agate pictures to tips@wire-sculpture.com, and they could be featured!

Resources

• http://en.wikipedia.org/wiki/Botryoidal
• http://mindat.org
• http://www.glypticconcepts.com/turtleback.html
• Peterson Field Guide to Rocks and Minerals by Frederick H. Pough, ISBN 0-395-91096-X

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by Rose Marion, Wire-Sculpture.com

Agate, one in a Series on Quartz

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About Agate

Generally agate’s hardness is a 6.5-7 on Moh’s scale, with a waxy luster. Although some agates have the appearance of glass, it is much harder: glass is typically only as hard as a 5.5. Agate is quite abundant and most varieties are very inexpensive, yet some still use glass to imitate it; a simple scratch test will prove whether it’s agate or glass. Many glass marbles are made to imitate agate, and there are also many beads on the market sold as imitation agate. Agate typically appears in gray, blue, yellow, or brown shades, and sometimes red; green and blue are the most rare of agate colors. Agate takes dye and color treatments well, which I will discuss along with geodes; however, bright and neon colors such as bright blue, bright purple, bright pink, etc are indicative of dye.

Idar-Oberstein, or at the time Oberstein, Germany, was the biggest name in cutting and processing agates, dating back to 1497. This included cutting European imports of South American agate, and dyeing. Low-cost energy provided by the Nahe river ran the cutting and polishing machines, and labor was inexpensive. Oberstein prospered until local gemstone finds dwindled; many laborers left for Brazil and other South American gem excavation sites, creating a new gem economy. While Oberstein has recovered in the years since WWII, it has steep competition from Thailand and India.

There are many forms of agate; this week is on riband agate, in which the layers of agate are parallel to each other.

Banded Agate

Many of the agates we’re used to seeing, for example Blue Lace agate and Botswana agate, have distinctive banding: light lines running through the dark piece (sometimes the hues are reversed). Sometimes this banding is so tight that it causes a rainbow effect, which you can see in this picture (click). While a neat effect, it usually doesn’t have an effect on the agate’s value or price.

Banding is typically very small, and the bands are typically the same thickness, end to end. Some are so small they can only be seen under microscope. Banded agate is called "fortification agate" when the banding is an angular circle shape: that is, the banding forms closed shapes that are reminiscent of a birds-eye view of a bastion or fortress with surrounding walls. There also other types of banded agate that are named for the appearance of the banding formation: eye-agate, ruin-agate, star-agate, shell-agate, coral-agate, and cloud-agate (which has cloudy patches against the transparent stone).

Brecciated Agate

Brecciated agate (click to see an example) is a kind of agate which has chunks of rock, rather than banding. "Brecciated" simply means broken rock, so while brecciated jasper is rock formed form pieces of jasper, brecciated agate I formed from pieces of agate that are then formed into a new rock. One example would be caused by an earthquake. A piece of formed agate rock is broken in the earth by an earthquake. Then over time, quartz forms around the agate pieces, such as amethyst or another quartz. This results in brecciated agate, which appears to have "chunks" of agate embedded in the stone. This kind of agate is sometimes called "ruin agate," because it resembles the ruins of buildings. The original agate and the surrounding material are often in contrasting colors,

Next article will cover agates that have "dots" rather than banding, such as bloodstone, fish-egg, polka dot, and orbicular agate. Have you made jewelry with any "dot" type agate? Send your agate pictures to tips@wire-sculpture.com, and they could be featured!

Resources

• What Is a Round Marble Made of Color-Streaked Glass Called?
• http://en.wikipedia.org/wiki/Agate
• http://en.wikipedia.org/wiki/Idar-Oberstein
• Precious Stones by Max Bauer, ISBN 0486219119

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by Rose Marion, Wire-Sculpture.com

Cryptocrystalline Quartz Introduction, one in a Series on Quartz

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As you have become aware in recent months, there are many, many kinds of quartz dug from the earth’s surface! However, it wasn’t until the 1800s that the many kinds were recognized as all having the same substance, SiO2, making them all quartz. This was discovered by the Swedish chemists Bergmann and J. J. Berzelius.

The old system of categorizing quartzes broke quartz into 3 types: Macrocrystalline quartz, which develops as visible crystals (as we’ve discussed: examples are citrine, amethyst, and smoky quartz). Microcrystalline quartzes (agates) are made of tiny crystal grains that can be seen with a microscope. Cryptocrystalline quartz crystals (carnelian, chrysocolla) are so densely packed that they can’t even be seen with a microscope! We’ve used this system to discuss the quartzes in the gem profiles, and will continue to do so. However, in modern days, “quartz” typically refers to macrocrystalline quartz, while cryptocrystalline quartz is called chalcedony.

And yes – Jasper is often categorized under Chalcedony (kal-sedn-ee): Dale has discussed the jaspers in great detail in Gem Profiles starting here.

How are Macro- and Cryptocrystalline Quartz Different?

How is macrocrystalline quartz different from the crypto- and microcrystalline forms of quartz? First, let’s look at the outside appearance. Macrocrystalline quartz like amethyst and rose quartz are generally transparent-translucent, whereas cryptocrystallines like agates are more often opaque. Agates and cryptocrystallines can be slightly softer than macrocrystallines, 6.5 on Moh’s scale rather than a full 7. Cryptocrystallines have a duller, wax-like luster while microcrystallines have a shiny, vitreous luster.  And Cryptocrystallines have a higher water content as well as other non-quartz ingredients, up to 20% more.

Because the cryptocrystalline quartzes can include several non-quartz minerals, many of these quartzes are considered “rocks,” rather than macrocrystalline amethyst, citrine, tigereye, and smoky quartz, which are more likely called “gems” or “stones” due to their purity.

Besides how they appear finished, the difference lies in how the quartz is formed. Generally speaking, in macrocrystalline quartzes like amethyst and phantom quartz, the quartz forms by adding molecules to the surface of the crystal, one layer at a time, jutting out into the surrounding environment. However, cryptocrystalline quartz emerges from a silica and water solution, usually formed precisely to its mold.

Types of Chalcedony (Cryptocrystalline)

Other types of chalcedony, besides agate, include, Carnelian, Chrysoprase, Onyx, Thundereggs, Petrified Wood, and some include Aventurine. Chalcedony is found all over the world, including in each of the 50 states. Chalcedony has been used since the Bronze Age, and was especially common along the Mediterranean: in jewelry, beads, and even wax seals – because hot wax would not stick to it. The name of chalcedony comes from the town Chalkedon, which is in present-day Istanbul, and was formerly an ancient Greek village. Idar-Oberstein, a German town, became renowned in the 19th century as a major chalcedony and agate processing center, preparing and dying the stones for carving and jewelry making. Many chalcedonies, especially agate, take dye very well, and some are heat-treated, such as carnelian, to deepen the coloration.

Agate is a variety of quartz (classified as chalcedony) that’s characterized by its fine banding and bright colors. Agates are typically about 90% quartz and 10% impurities and moganite, also SiO2 but in a different structure than quartz. Agates are associated with volcanic activity and can be found in metamorphic rocks. Agate’s been used in making jewelry and carvings for millennia, having been discovered along the Achates River in Sicily over 3,000 years ago.

Agate often fills cracks or veins in volcanic rock, or cavities in cooled lava – it can even be found in dinosaur bones. Many agates do not fill completely, in which case druzy quartz crystals can form. In fact, sometimes amethyst crystals will form! There are dozens of varieties of agates, including fire agate, tree and moss agate, plume agate, and the agate geodes I mentioned. I’ll be discussing some of these next week – send your agate pictures to tips@wire-sculpture.com, and they could be featured!

Resources

• http://www.quartzpage.de/gen_types.html
• http://en.wikipedia.org/wiki/Quartz#Microcrystalline_varieties
• http://en.wikipedia.org/wiki/Chalcedony
• http://www.rps.psu.edu/0109/form.html
• http://www.agatelady.com/agate-basics.html
• http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/chalcedony.html

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