Identifying Agates and Chalcedony the CORRECT Way:
There has been some so called "resources" that I have personally read and watched that often gives you misidentified examples of incorrect names or types for a certain Agate or Chalcedony.
First off, the difference between Chalcedony and Agate is that Agate is the sub variety of Chalcedony, but Chalcedony in itself is a solid hue or colorless of the variety of the mineral Quartz. Some videos I have seen on YouTube would describe agate as a "different" mineral than Quartz, which in fact Chalcedony, Agate, and Quartz is identical in every way except the physical characteristics (physical shape that you see) and that Agates and Chalcedony are in fact "cryptocrystalline;" meaning microscopic crystals.
All three is Silicon Oxide (SiO2); but the contents of trace elements could be different within each individual specimen. They typically form the same way, but with Quartz (rock crystal) itself is formed slightly different. Agates and Chalcedony is formed as a silica gel-like substance that seeps into hallow cavities within Basalts and other host rocks during the formation process.
As for species of Chalcedony and Agate, you got different colors and patterns within each "family." Say an Ellensburg Blue is actually without any bands in it would be considered Blue Chalcedony, while WITH lines in it, that would correctly be called Blue Agate. It's really about the patterns and lines determining the correct terminology. Another example, Carnelian; people confuse it as "agate" when it really is just a red to reddish orange, or brownish orange color variety of Chalcedony. If it was to have lines in it, then it would be agate. These are just some details to be considering when you want to get the terminology correct.
ALL Agates and Chalcedony has a waxy luster to it. Making it almost looking like a hard clump of (transparent, translucent, or opaque) waxy mass. Pitted surface is caused by the erosion of the main host rock (usually basalt).
Are Agates and Chalcedony rare?:
Simple answer is "no," they are not rare. The only parts in the Quartz family that is anything rare is what the inclusions are within the Quartz, or Quartz related stone. Such as a variety of Dumortierite (a blue radiant crystal) inside a perfectly terminated Quartz specimen would be rare. Not in the mass form of Dumortierite Quartz some people get confused for Lapis Lazuli) is not rare. Also another example is called "Petro-Quartz;" a Quartz crystal with petroleum inside as the inclusions is rare. While Quartz itself is incredible common. Agate and Quartz is simple not overly rare. Some in fact ARE more rare than others like natural untreated Blue Agates, or natural untreated Chrysoprase (green chalcedony colored by the element nickel) are more rare than traditional Agates. When somebody says: "This Agate is 'super rare' and hard to find." They're just pulling your leg; Agates in general are not rare what-so-ever. If Agates are rare, have you personally seen an Agate go for $1000/ct. when it is a little bit larger than a golf ball? These are kinds of questions to ask yourself if you are unsure.
-Agates range from $.50/ct.-$37/ct. or $5/lbs.
-Chalcedony can go from $2/ct.-20/ct.
-Natural Untreated Blue Chalcedony between $10/ct.-$25/ct.
-For All sized cabochons of Chrysoprase from $8/ct.-$20/ct (depending on color)
Properly Identifying Carnelians:
It is very simple to identify Carnelians, but to properly identify Carnelians is easy to get wrong. Carnelians are simply just the both Chalcedony and Agate, but with a color that can only range within the hues of Yellow-Orange, Red, and Orange-Brown. If it ranges in the Yellow hues, it is simply NOT a Carnelian, this is what is known as Yellow Chalcedony, or Honey Chalcedony (or Agate if it has lines or Agate-like patterns). All the colors is due to presence of Iron. Darker colors means there is more traces of Iron within the molecular structure (or lattice). If you are a beginner, this information will help you properly identify a Carnelian from a Yellow Chalcedony (or Honey Agate) then a "Yellow Carnelian." To be a true Carnelian, there must be a Orange hue (either primary hue or secondary hue). If it ranges to a reddish-brown with no hues of orange, then this is called Sard.
Prices for Carnelian is around $.50/ct.-$20/ct.
Carnelian of intense fiery orange, would command at the higher end of the price range.
Picture on the left: True Carnelian, primary hue is orange. Picture on the right: Yellow Chalcedony. Insufficient amount of orange hue to be classified as Carnelian
Other color Agates and Chalcedony:
Not only do they just come in various earth-tones, but they even come in pinks, purples, greens, and blues.
The most popular blue variety of both Agate and Chalcedony (in the State of Washington) is the Ellensburg Blue. The E. Blue (as some call it) is a beautiful is what Central Washington University (CWU) thinks this is done by the refraction of light particles in the stone. Almost the similar way why the sky is blue. This process in nature is more uncommon then why Sapphires are blue (titanium and iron elements within the crystal structure). Unique geology behind the color of these particular Agates and Chalcedony is why they are valued at most $25/ct. (faceted) Their color is highly sought after by collectors and jewelry designers alike.
If any Agate/Chalcedony is to be rare, it would indeed be the natural untreated blue colors (such as Blue Chalcedony from other localities around the world; and Washington's own Ellensburg Blues, that is only found only in the Kittitas County),
Something about a "natural blue rock" that just fascinates people.
Chrysoprase (sometimes referred to as "Prase") is the nickel rich variety of Chalcedony. The element nickel is also what is responsible for the green of Chrysoprase. Apple green variety is the most valuable then those of the lighter green hues. Not to be confused with Green Onyx, which is colorless Chalcedony stained by green dyes. Same goes for any other color of Chalcedony that may be dyed.
