18 January 2013

Unexplained "sand spike" concretions

Excerpted from Oddities of the Mineral World (Van Nostrand Reinhold Company, 1976.)
No discussion of concretions would be complete if mention were not made of a real puzzler, a truly unique type of concretion that apparently remains unexplained—sand spikes...
Briefly, the locality consisted of a series of low, sandy hillocks and banks near the Mexican-American border close to Mt. Signal, Imperial County, California. When they were first discovered, many of these unique concretions were weathering out on the surface of the ground. It became apparent, however, that there actually were beds of these strange concretions 3 feet to 8 feet underground!
These concretions consist of a ball-like end coupled with a tapering spikelike formation. In uncovering a bed of spikes over 95 percent of the formations were found pointing west. Spikes of similar types or formats seemingly occurred in the same bed or within lenslike concentrations of the sand-spike formations...
They are composed of absolutely nothing but the identical sand forming the soft little hillocks and banks in which they occur—solid sandstone with no fossil material inside. The mineral cementing the grains together is apparently calcite.
What are they? No one really knows—other than they obviously fall under the heading of concretions by virtue of their method of occurrence and basic mineralogical composition. The long points, westerly oriented, are the most provocative aspect of this truly unique locality. Some say that they are fossils of an ancient type of bulbous seaweed that drifted heavy-end eastward on some ancient shoreline... It has also been suggested that they are some type of fulgurite, which is positively incorrect, and not by any stretch of the imagination are they prehistoric man-made artifacts.
See also this 1934 article in Rocks and Minerals and this one from the American Journal of Science in 1936.

Via Allan McCollum and The Agateer (newsletter of the Madison Gem and Mineral Club).


  1. I found something very similar to this near Abilene, TX. When I picked up the last one, I got violently ill from heat (from air temp, not the stone)and I always wondered if I'd hallucinated the conical sandstones. I hope someone has some insight about them.

  2. They look too regular to be fulgurites.

    1. I think if they were fulgurites the sand would be fused to more of a glass-like consistency.

  3. apparently there are some twisted ones, too


    while others show a ridge and turned pattern


    1. That second link offers a nice point-by-point debunking of some of Hancock's material. Blogworthy for a linkdump post later. Thanks.

  4. It reminds me of a project to use lens condensed sunlight on sand for 3D printing: http://www.youtube.com/watch?v=ptUj8JRAYu8

  5. My initial thought process led me to lightning strikes also. That much energy and heat would quickly congeal silica into a concretion. The type of concretion depends on several mineral content factors in the ground.

    As to the pointing west part, I would be curious to know which direction the river was running where these items were found. Any swift running water would turn the concretions so that the pointy end with least resistance face upstream.

  6. it almost looks to me like 'drops' of super-viscous semi-liquid that 'dripped'...

  7. Two factors that might help explain it. That area is very unique in north America.
    (1) The San Andreas Fault is right there. These would be on the Pacific Plate side.
    (2) That part of Imperial County is also below sea level. That area is the heart of a great rift valley, like the one in Israel and the one on eastern Africa.

    My point being that there are some very powerful and unique geological forces at play in that exact spot.

  8. They are just a different shape. But they are a concretion. I have several that look this way in my collection.


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