Friday, September 30, 2016

Rubellite from Pala, San Diego area, California

Rubellite, a gemstone variety of the mineral tourmaline, can be transparent and possesses a beautiful reddish pink to violet or light green color. It can also be nearly colorless.  One of the best known localities for this gemstone is in the Pala mining district, at Pala, near San Diego in southern California. About 10 years ago, I was a member of a group of geologists invited to tour the historic Stewart Mine at Pala. We were allowed to search through discarded diggings, but I was able to find some nice specimens that were not too weathered. It is important to mention that this mine is on private land and getting permission to enter the land is absolutely needed.

The individual crystals of rubellite on the left side of the picture are approximately 1 cm in height. The ones that appear somewhat blackish are transparent enough to show the black color of the background material on which they were photographed. The cluster of weathered crystals on the right is 5 cm in width. 

Rubellite from the Stewart Mine is commonly in a matrix consisting of the lithium-bearing mineral lepidolite (it is purple and shines a lot like mica). The cluster of rubellite shown above is in lepidolite.

The rubellite in the Stewart Mine is found in a complex and highly mineralized granitic pegmatite-aplite dike. 

Tuesday, September 13, 2016

The world's oldest fossils (maybe).

In September of 2011, the discovery of the so-called "world's oldest fossils" was written up in   Nature Magazine, mentioned in newspapers, and discussed online.

These "fossils" are 3.7 billion years old and were found in southwestern Greenland following recent melting of some snow. They might be stromatolites made by cyano-bacteria, and, if so, they would be 220 million years older than previous substantiated previous finds of Precambrian cyano-bacteria.

I include the best picture I could find online showing these Greenland "fossils."

The Greenland "fossils," 1 to 4 cm high. Picture credit: Allen Nutman/Nature Magazine. To see more information about these "fossils" go to <>
Upon seeing the photo above, my immediate reaction was that they might be flame structures, which are sedimentary (non-organic) structures created by dewatering of "soupy sediment" when it is compacted. The sediment literally is squeezed into the overlying sediment and "flows" as it does, creating the appearance of "flame tips." Flame structures can be of any geologic age.

I include a picture of a flame structures in an outcrop that I came across several years ago while doing some geologic mapping. This example is in deep-sea turbidite deposits in the lower Pliocene Towsley Formation in northern Los Angeles County, southern California. You will have to admit, at least, that the resemblance is striking.

A flame structure (closeup shown on the right) in the Towsley Formation just north of Sunshine Canyon, Santa Susana Mountains, southern California. The staff is 1.5 m in length, and the flame structure is a few centimeters high. Note: There is a watch (for scale), without a band, on the talus slope just left of the flame structure.

Thursday, September 1, 2016

The "ins and outs" of two snail shells with tall spires

Sectioning a seashell longitudinally can reveal some interesting internal details, and these can be highly useful for the identification purposes. In the case of Telescopium, notice the presence of an indentation (fold) on the inside of the aperture (the large opening at the anterior end of the shell). This fold is also present on most of the height of the central axis (columella) of the interior of the shell.


Exterior and interior views of modern-day specimens of Telescopium telescopium (Linnaeus, 1758) from Indo-Pacific mangrove mud flats. Height of shells approximately 3 inches.

Although Turritella superficially resembles Telescopium, the columella of Turritella does not have an indentation. The aperture of Turritella is round and without a fold.


Exterior and interior views of modern-day specimens of Turritella cerebra (Linnaeus, 1758) from Indo-Pacific shallow-marine waters. Height of shells approximately 4.5 inches.