Oklahoma Agates/ flints

Howdy, I think we've discussed this here before so you might read back through some past posts but basically agate and flint are both microcrystalline quartz but flint and chert come from marine sedimentary formations where they frequently form as nodules in limestone, chalk etc or as meta-silicates where sediments have been infused with silica ( chert), whereas agate usually forms from silica deposition in cracks and pockets in volcanics like basalt and rhyolite. Therefore we find lots of agate in the mostly volcanic west while there in the old middle American marine beds you guys find all the flint and chert....mel

Some facts garnered from a favorite site of mine: www.rings-things.com/gemstone/c.htm#chalcedony

Flint, agate, jasper, chert: it is all quartz, a family of minerals with the same chemical composition (silicon dioxide) and similar physical properties. The two varieties of quartz are macrocrystalline (crystals recognizable with the naked eye) and microcrystalline or cryptocrystalline (crystals too small to see without high magnification). Macrocrystaline quartz includes citrine, amethyst, aventurine, hawks-eye, tigereye and other common quartz crystal stones (flake, rutilated, rose, smoky, snow, etc.). The second, cryptocrystalline, is more commonly known as chalcedony.

Chert, flint, and jasper are on the opaque side of the chalcedony quartz varieties, while agates (and sub-types of agate such as onyx) are translucent or transparent. Chalcedony is a catch-all term for cryptocrystalline quartzes (quartz with microscopically small crystals). The chalcedony family as whole includes agate, jasper, carnelian, chrysoprase, onyx, bloodstone, aventurine, flint, chert and sard.

Chalcedony forms in rounded crusts, rinds or stalactites in volcanic and sedimentary rocks. The most common forms are agate and jasper. As a marketing term in the gemstone industry, however, "chalcedony" has come to acquire a more limited definition. The name usually refers to semitransparent or translucent chalcedony with a solid color (commonly pale bluish-gray) and nearly waxlike luster. The color can also be white, blue, purple, pink, yellow, orange or red (but not orange-red, as that stone is known as carnelian). Blue and purple are the most popular hues. Chalcedonies can be either transparent or translucent, solid or patterned.

Agate is usually translucent and has clearly defined bands and markings, while jasper is generally opaque, more irregular and less defined. No gemstone is more creatively striped by nature than agate. This distinct and dramatically banded variety of chalcedony is composed of quartz layers. The Greek origin of the word jasper, iaspis, means "spotted stone." This form of semiprecious chalcedony, or microcrystalline quartz, is usually red, brown or green. Its patterns are much less regular and defined than those of the other chalcedony variety, agate.

A key difference between jasper and agate is that jaspers are generally opaque, while agates tend to be translucent (or at least contain translucent bands). This distinction stems from the stones' composition: Jasper contains microscopic "grains" of crystalline quartz and agate has microscopic "fibers" of crystalline quartz.

An interesting chalcedony concept is pseudomorph, the atom-by-atom replacement of one mineral for another without changing the original mineral's external appearance. Petrified wood is a well-known example. In the Petrified Forest National Monument of Arizona, the remains of an entire ancient forest was transformed into chalcedony. Petrified bone is another chalcedony pseudomorph. The process is nature's preservation of an organic substance in its original appearance. Pseudomorphs of inorganic substances also occur, such as when agate replaces dog-tooth calcite. Mexican crazy lace is an example. A common macrocrystaline quartz pseudomorph is tigereye. Tigereye is a quartz with rich yellow and brown stripes, and a fine golden luster. When viewed from the opposite direction, the colors are reversed. It contains oriented fibers of crocidolite (a mineral of the amphibole group) that have been replaced by silica.

Thanks for the info,
Being very new to this hobby there is so much to learn. I am constantly reading about rocks and their make up etc.. I hate reading but for some reason, this hobby really interests me, so I find myself picking up books and reading about the rocks and minerals and gems I see pictures of. I wish we had better books here at the house to find out what our rock collection is made up of. We have some very very rare rocks from all over the world. some have I.D. number labels on them but unfortunately when Betty as given this collection the identification book was not with the rocks and gems. so we have been on a quest to find out what is what. not an easy task. the pictures in the rock collectors books are not always like the rocks we have and the definitions and write ups are not too good either for what we are looking for.
WE are really getting into this though, it keeps us busy and is fun.
Thanks for everyones input on the flint and agates.
Steve & Betty