Report: Stalk Aggregate Agates

On one of my 2018 rock hunting forays on ‘The Carver’ agate field in west Texas, I happened to pick up two specimens which, when cut, I could not identify.  After research, I concluded that they were ‘stalk aggregate agates’ –quite a mouthful.  These were not something I had seen or heard about before this discovery.

After cutting them vertically and horizontally, their appearance varied greatly depending upon the direction of the cut.  Photos #1 (2679) and #2 (2683) show two examples of the stalk aggregate cut vertically.  Photo # 3 (2767) shows a cross-sectional cut of the specimen shown in photo #1, creating an ‘eye’ similar to the look of an eye agate.

Agate expert, Pat McMahon, describes stalk aggregate agates as being formed “when a material of lesser density like water rises up through a viscous gel-like medium of greater density,” such as a silica gel.  He goes on to say that they are “stalactitic in appearance and their growths are parallel to each other.”  [Pat McMahon Agate Collection, page 17].  This stalactitic appearance can be seen in both the interior of the rock specimen, photo #2 (2683), and on the exterior of the specimen photo #4 (2685).  These two different specimens are the only exemplars of the stalk aggregate agate found thus far on ‘The Carver’ agate field.

Photo #1
Photo #2
Photo #3
Photo #4