What are agates? "Agate is the banded form of the mineral chalcedony, which is a microcrystalline variety of quartz. Agate is the most varied and popular type of chalcedony, having many varieties on its own," according to minerals.net.
Beyond the formal definitions, agates are fun! They are common and abundant and can be collected almost anywhere. No matter where you live, there is probably an agate field within easy reach for a day trip.
Their abundance makes most agates inexpensive at rock shops and gem shows. Plus, they can be enjoyed “as is” or cut, crafted, and tumble polished into lapidary wonders.
What are agates? The perfect stones for the beginning collector!
How are Agates Formed?
The best thing about agates is the variety they show in colors and patterns. An agate may grow as an undifferentiated mass. It may be all one color, or it may have inclusions or colorful concentric bands.
Agates precipitate out of solution and grow in seams within other rocks or within vesicles in basalt or cavities within limestone, later eroding out as nodules.
What are Agates? List of Common Varieties
While there are many, consider a few of the more common varieties.
Fortification agates have concentric bands that look much like a “fort” circling a castle.
Waterline (or water level) agates have straight bands that were formed by gravity as layer after layer of agate was set down.
Eye agates have spots on the surface.
Flame and plume agates are very similar. Flame agates have swirling red lines that look like fire, whereas plume agates have interesting inclusions that look like ferns or plumes of smoke.
Sagenitic agates have inclusions, but these are needle-shaped.
Moss agates are similar to plume agates, but the plumes permeate the entire rock, often in shades of green, brown, yellow, or red.
In addition, there are shadow, tube, seam, polyhedral, enhydro, fire, iris, and many more varieties of agates. This wonderful variety makes agates a whole lot of fun to collect!
Look through the agates in your own collection. How many varieties can you spot?
This Rock & Gem Kids column about what are agates appeared in the August 2021 issue of Rock and Gem magazine. Click here to subscribe!