Why are agates more rare?

[rockjunquie]

Is there a simple reason why agates are more rare than a jasper or rhyolite, for example? I'm probably showing my ignorance, but I've always wondered about this.

[woodman]

But are they? I think that may depend on where you looking.

[knave]

Tela do you know why one side of the VEE is always longer when the geese are flying?

[knave]

We can find 50 jasp/agates around here for every real one

[rockjunquie]

Feb 5, 2020 20:46:33 GMT -5 woodman said:

But are they? I think that may depend on where you looking.

Yeah, everywhere I read says you don't find as many. That's one reason why they cost more.

[Deleted]

Feb 5, 2020 20:46:33 GMT -5 woodman said:

But are they? I think that may depend on where you looking.

I agree. Even defining what is an agate and what is a jasper is a vexed subject. To mineralogists and geologists, they are both just chalcedonies (micro-crystalline quartz + various impurities). Gemologists have varying definitions (some cling to the "if it ain't banded, it's not an agate" cliché, some allow for plain chalcedony containing various inclusions, such as moss, to be considered agates), and patterned stones generally are dismissed by a narrow-minded, goodly portion of the gemological types who know little beyond diamonds (and maybe a bit about corundums and emeralds) - no matter that collectors pay high prices for some agates, jaspers, and rhyolites. Mass market jewelry manufacturers tend to only look at stones that all look nearly the same for their matched sets and cookie-cutter designs, so that's where the focus has stayed.

As you said, rarity depends on what is in the area, and also what qualities you are looking for in an agate, jasper or rhyolite. Some agates are scarcer than others, some jaspers are scarcer than others, some rhyolites are scarcer than others. The bulk of all 3 materials have few or no gem-worthy qualities.

Price often doesn't follow true rarity, but rather fashion meeting small output from a particular source. At one time, when local jewelry stores produced their own, unique pieces, patterned gems were in higher demand. Seemed to be a big change during the 70s with mall jewelry chains crowding out the mom and pop shops. I think there is developing greater appreciation among the younger set for unique items than there has been for decades, so perhaps there is hope for a revival of interest in these gem materials. A lot more kids these days know that diamonds aren't all that rare (and can now be manufactured on demand relatively inexpensively).

[joshuamcduffie]

Feb 6, 2020 0:34:03 GMT -5 knave said:

Tela do you know why one side of the VEE is always longer when the geese are flying?

'cause there are more geese on that side?

[Fossilman]

I think agates are more popular than other material, making the market push more with value..

Here is a site that might interest you..

www.gemsociety.org/article/agate-gem-information/

[rmf]

Simple answer: Agates are made in batches like cookies. Rhyolites are made in cement mixers like a volcano.
In lapidary “Jaspers” are frequently not true jaspers. Like leopard skin jasper not a true jasper but it has been given a marketing name.

People do this a lot to help things sell. Like Mexican Onyx (Not Onyx at all but Travertine). A good example (and a pet peeve of mine) is “Organic Food”. By definition all food is organic since there are only organic and inorganic substances. Someone just decided to call using no pesticides and no commercial fertilizer as “Organic” for marketing, hoping to sell more at a higher price. Go into Walmart and ask for the inorganic bananas and see what you get.

[rmf]

Think of Chalcedony as pure Agate with no minerals for color. Chalcedony is composed of Cryptocrystalline silica but it is not all Quartz though it is all SiO2.
In minerology some minerals have more than one crystal form(habit) and the crystal shape make a difference in its physical properties. Chalcedony is composed of Moganite and Quarts.
Moganite is SiO2 crystalized in the monoclinic crystal system.
See en.wikipedia.org/wiki/Moganite
Quartz is also SiO2 crystalized is the Hexagonal system.
Chalcedony is very fine crystals of these two minerals intertwined in a 3-d matrix. That is what gives chalcedony its Luster (Waxy, vitreous, dull, greasy, silky).

Now add some local minerals for color, and texture and you have Agate.

My opinion is that Agates are God's specialty (as far as rocks are concerned). Rhyolites and Basalts (Host rocks to hot water Agates like Brazilian and Lake Superiors) are generally made by volcanic activity. Keep in mind Granite and Rhyolite are composed of the same stuff it is just a matter of crystal size. Crystal size is determined by rate of cooling. The smaller the crystal the quicker it cooled. Hot water Agates are typically gas bubble fillings. I have seen lakers still in rhyolites and it is my understanding that Brazilian agates are from Basalts.

Cold water Agates are made on the ocean floor from silica jell. From what I have read (sorry do not have any doc to back this up right now) silica jell is from really small critter carcases that fall to the ocean floor. These form a jell and under the "right" conditions they make agates and some Chert/Flint. In TN we have all kinds of chert but little Agate. Chert is wide spread but Agate is restricted to middle TN and on the back side of the Cumberland Plateau. KY Agate, TN Agate and AL Paint Rock Agate all formed in the same ocean at the same time just different local minerals cause the different colors and patterns.

[knave]

Wow rmf, mind blown that is 99.99% pure information right there...

ETA: and i had the joke about the geese. So much to learn about rocks

[whyofquartz]

Feb 6, 2020 2:22:54 GMT -5 @rocks2dust said:

Feb 5, 2020 20:46:33 GMT -5 woodman said:

But are they? I think that may depend on where you looking.

I agree. Even defining what is an agate and what is a jasper is a vexed subject. To mineralogists and geologists, they are both just chalcedonies (micro-crystalline quartz + various impurities). Gemologists have varying definitions (some cling to the "if it ain't banded, it's not an agate" cliché, some allow for plain chalcedony containing various inclusions, such as moss, to be considered agates), and patterned stones generally are dismissed by a narrow-minded, goodly portion of the gemological types who know little beyond diamonds (and maybe a bit about corundums and emeralds) - no matter that collectors pay high prices for some agates, jaspers, and rhyolites. Mass market jewelry manufacturers tend to only look at stones that all look nearly the same for their matched sets and cookie-cutter designs, so that's where the focus has stayed.

As you said, rarity depends on what is in the area, and also what qualities you are looking for in an agate, jasper or rhyolite. Some agates are scarcer than others, some jaspers are scarcer than others, some rhyolites are scarcer than others. The bulk of all 3 materials have few or no gem-worthy qualities.

Price often doesn't follow true rarity, but rather fashion meeting small output from a particular source. At one time, when local jewelry stores produced their own, unique pieces, patterned gems were in higher demand. Seemed to be a big change during the 70s with mall jewelry chains crowding out the mom and pop shops. I think there is developing greater appreciation among the younger set for unique items than there has been for decades, so perhaps there is hope for a revival of interest in these gem materials. A lot more kids these days know that diamonds aren't all that rare (and can now be manufactured on demand relatively inexpensively).

I had been wondering about this for a very long time. In short it seems Agate is in the eye of the gemholder.

[Benathema]

rmf said:

Go into Walmart and ask for the inorganic bananas and see what you get.

A lump of potassium, a salt shaker of transition metals, and a lump of sulfur to get your dose of yellow?

[Deleted]

Feb 6, 2020 10:33:51 GMT -5 Fossilman said:

I think agates are more popular than other material, making the market push more with value.

Probably by volume more than any per-piece value. A large percentage of the agate in the "jewelry" marketplace is otherwise non-descript material that is dyed to order - producing the matched colors that mass-market manufacturers prefer. Few of even the high-end jewelry firms use much of the agate types that are truly rare.

I no longer trust those gems - of any type - sold in most stores, as too much of the stuff now offered is lower quality that has been artificially colored, fracture-filled, clarity-enhanced, etc. - when it's not outright artificial or fraudulently represented. Started online, but now it is everywhere and the attitude of the people heading the organizations that are supposed to be monitoring the jewelry industry - um, I feel a side-track rant coming on, nope, not going to do it now. I'll just observe that folks here are lucky to be handling REAL stuff, and know or be learning the difference.

[rmf]

Actually agates differ from jasper in the size of the silica. which makes it hard to determine the difference unless you train your eye to look for those things. Even then mother nature has a way of making it difficult to the unaided eye.

Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically[1][2] in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are cryptocrystalline. Carbonado, a form of diamond, is also cryptocrystalline. Volcanic rocks, especially of the acidic type such as felsites and rhyolites, may have a cryptocrystalline groundmass as distinguished from pure obsidian (acidic) or tachylyte (basic), which are natural rock glasses. Onyx is also a cryptocrystalline. Agates such as the fairburn agate are also composed of cryptocrystalline silica. From:https://en.wikipedia.org/wiki/Cryptocrystalline

Where as Jasper is: Jasper, an aggregate of microgranular quartz and/or chalcedony and other mineral phases,[1][2] is an opaque,[3] impure variety of silica From: en.wikipedia.org/wiki/Jasper

So the difference in Agate and jasper is one is interlaced very fine crystals interlaced like fibers and the other (Jasper) is made of much larger grains mashed together like a very fine quartzite. I am thinking micro indicating a millionth of an inch.

[Deleted]

Feb 6, 2020 21:01:00 GMT -5 rmf said:

So the difference in Agate and jasper is one is interlaced very fine crystals interlaced like fibers and the other (Jasper) is made of much larger grains mashed together like a very fine quartzite.

Except when that isn't the case. Some jaspers (as well as flints and cherts) don't fit that definition at all. There are jaspers which ring, fracture, are highly translucent, and appear under high magnification just as do some agates (which also do not fit neatly into the definitions some have attempted to impose upon them). That there are not neat boundaries is why the arguments as to what makes an agate and what makes a jasper or flint will continue on, and why mineralogists and geologists mainly just throw up their hands and designate them all as chalcedony and leave the conflicting definitions up to traditions rather than impose some sort of absolute systematization. A similar situation exists with corundum (ruby or sapphire), beryl (goshenite, green beryl, chromium emerald, vanadinite emerald, maxixie, blue beryl, bixbite/red, morganite, heliodor), and other distinctions that have more to do with imposed distinctions based upon things like color than with differences in makeup or structure.

[RocksInNJ]

I find it easier to just call them pretty or ugly rocks. Keeps it simple. 

[Fossilman]

The most expensive agates I run into on the west coast, are Montana moss agates... Some think this material is gold and want over $12 a pound for it!
I usually wait till I head back home to Montana to visit and hound a bit , can get it there (only place it comes from) for a few dollars a pound and sometimes just given to you...

[roy]

as with jaspers you cut some slabs are the same all the way threw the rough and chunk after chunk this is not so with agate almost every slab off a rough can and will be diffrent and every agate is most often diffrent unless its a seam agate then this will not be true