Bullfrog Agate Report

Bullfrog Agate, named by me, reflects the specific single and small location where this unique agate is found on The Carver Agate Field, located near Alpine, Texas. Bullfrog Agate has a formative process which is different from the geodes, nodules, agates and jaspers found throughout The Carver. Bullfrog Agate is characteristically identified by the soft white (Rock #3952 photo below) rind, almost always surrounding a dazzlingly diverse array of colors (Rock #3909 photo below) and agate forms, which contain highly varied and spectacular sagenitic material.

Rock #3952 : Soft white rind

Rock #3909 : Dazzling array of colors

Gallery: Highly varied and spectacular sagenitic material and shapes

Rocks #3618, 3938, 4473, 4490, 4718, 4945, 4941, 5196, 5304, 5386, 5398, 726, 4771

Click each photo for an enlarged view.

The whitish rind (Rock #3486 photo below) appears to be volcanic ash in which these agates were formed. This rind is ash that has been compressed and hardened by pressure and the hardening of a water/silica solution that permeated the ash, and ultimately filled the voids in the ash with beautifully colored agates and highly variable sagenitic material.

Rock #3486

Rock #811
Bullfrog Agate cut and polished slab cross-section


The voids in the ash were not the same as the voids in lava, which are the most common source of the nodules, geodes and agates found on The Carver. Field specimens display highly varied specimen shapes due to the highly variable shape and size of the voids in the ash where formed. See photos of Rocks 4158, 1620 , 1619, 1617 below. Click on each photo to enlarge it.

The presence of pressure in the formation of Bullfrog Agate is seen in the obvious and extensive cracking and breaking of some of these specimens. See photos of Rocks 2748 and 2749 below.

Rock #2748

Rock #2749


Note some reformation after cracking is seen in the photos above.
Click on each photo to enlarge it.

In many cases, the silica mineralization also caused the agatization of and within the whitish rind (See photo of Rock #5383 below).

Rock #5383

Rock #3487 : In rare cases, a geode may form in Bullfrog Agate

Rock #3486 : See whitish rind and varied shape

Gallery: Variably shaped and sized specimens

Rocks 4158, 1620 ,1619 ,1617. Click on each photo to enlarge it.

Rock #2749 : See evidence of cracking from pressure

Rock #2748 : See agatization within the whitish rind

Rock #5383 : See agatization in the whitish rind

Gallery: Spectacular, beautiful and fascinating Bullfrog Agate cabs

Because the quartz/chalcedony containing the agatization within the rind is essentially the hardness of quartz, it is much harder than the ashy white rind which contains silica, but is primarily ash. Cutting, grinding and polishing two materials of different hardness in a single stone is always very challenging. But, if Bullfrog Agate is carefully and successfully cut, the results can be spectacular, beautiful, and fascinating as well as unique.

Rocks 4728, 3934, 3935, 3620, 4163, 4718: Click on each photo to enlarge it.

Bullfrog Agate specimens are much more interesting and beautiful if viewed on a large screen, particularly one with the capability of enlarging the photo.

Rock #3911 : Enlarge this photo by clicking on it.
The enlargement will clearly show the intricate and complex mineralization
and crystallization which has occurred in this material during formation

Having checked with three of my friends who have a long history and knowledge regarding West Texas agates, I am not aware of any other agate field in West Texas which produces Bullfrog Agate, named for its singular place of formation on The Carver Agate Field.