Agate: Another Crater jewelry rock


By Margi Jenks


As part of my continuing series on the other beautiful and interesting rocks to be found at the Crater of Diamonds State Park, this week’s topic is agate.  Although not as valuable as our diamonds, the Crater’s agate is still a beautiful stone and can be made into some lovely jewelry. 


Agates, like geodes, are openings that have been filled in by layers of quartz crystals and chalcedony.  Chalcedony is a type of quartz that is made up of very tiny quartz crystals; so tiny that they can only be seen by slicing the rock so thin that you can see through it using a high powered microscope.  Geologists call this type of tiny crystals, cryptocrystalline.  In agates the layers that filled in the openings generally alternate between the quartz crystals and the cryptocrystalline chalcedony.  The quartz crystals are usually clear, but the chalcedony can be a range of colors, from red to brown to green, depending upon the mineral that contaminates the chalcedony.  The most prized agates are those that have many thin alternating layers of different colors.
Sliced Crater agate with amethyst layers

Most agate originates from volcanic eruptions.  In the case of the Crater agate it appears to be the result of hot spring activity that followed the eruption of the volcano.  The agates look like they filled up cracks, rather than round holes we associate with geodes.  So, when I tell visitors how to find the agate I tell them to look for the “sandwich rock”.  The rock will usually be fairly flat and the top and bottom surfaces will be rust-colored.  I call that the “sandwich bread”.  Then, when you examine the side, you will find that it is very different--often white or golden or brown, and having a glossy surface.  This is the filling of the “sandwich” and the part that is the agate.


Humans have collected agates for eons.  The rock was named by the Greek philosopher and naturalist, Theophrastus, who found it on the shores of the Achates River sometime between the 4th and 3rd centuries B.C.  It was used in the art of hardstone carving at a number of ancient sites.  Archeologists have found carved agate in their excavations of the Bronze Age Minoan civilization on the island of Crete.  Today some lapidary experts cut and polish the agate into oval shapes and then wirewrap it to make lovely earrings and pendants.  We sell some wirewrapped Crater agate in our visitor center gift shop.  So, the next time you come to look for diamonds, also keep an eye out for the agate!  It is definitely worth taking home with you, even if you only use it as a pretty paperweight.

Crater agate wirewrapped pendant by Larry Macguire, Ida, Louisiana

Search area last plowed:  August 30, 2011; Most recent heavy rain:  September 18, 2011


Total diamonds found in 2011: 394

Diamonds registered for September 25–October 1 (100 points = 1carat): 

September 26 – Billy Russell, Noblesville, IN, 38 pt. white

September 27 – Joe & Betty Spivey, Eldorado, TX, 67 pt. white

September 28 – Richard Trent, Rusk, TX, 12 pt. white

September 30 – Jim Graham, Prescott, AR, 2 pt. brown

October 1 – Kenny & Melissa Oliver, Rosston, AR, 2 pt. white

Crater of Diamonds Home Page
209 State Park Road
Murfreesboro, AR 71958
Phone: (870) 285-3113

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