I was reading some garbage that a seller of fake meteorites had created to pass his piece of ordinary rock off as a meteorite. He went on and on about all the history of it and how it was the only piece like it on earth. All the normal con man stuff we see too often nowadays. But, mixed in was a short cut and paste discussion about micro tektites. I am convinced the seller knew nothing about micro tektites himself. But, it was just the thing I needed since I was having a little trouble coming up with something to write about this month.
It has been a couple years since I worked with my micro tektite rich rock from Haiti. So it is off into the world of the microscopic this month. Some of the readers of these monthly installments are aware that I have some very fine scales at my disposal. But, I have to admit that I am not going to attempt to weigh individual micro tektites. I think I have a scale that would do it. But I can no longer handle the tiny particles safely in and out of the scale. They are extremely brittle and over the years I have broken too many just trying to arrange them for photography on the microscope stage.
We talk often about small things being the size of the “head of a pin”. With micro tektites you need to begin thinking in terms like the point of a needle. These ancient drop of glass and their close cousins the spherules of minerals are often very tiny. The sphere shaped tektite pictured below is an average size. They are often much smaller. The tip of a sharp sewing needle does not appear very sharp but is, and the tektite is nearly as small as the diameter of the needle shaft.
I called it micro tektite rich rock but in actual fact it is not really rock. It is more like some kind of soil, a microscopic conglomerate. All these differing sized spheres and ovoid shaped tektites mixed very loosely with tiny particles of clay, shattered quartz, and the remains of devitrified micro tektite exteriors. The tektites are very ancient and most are not solid glass anymore. Nearly all the spheres have an exterior coating of white. The bubble types also have this coating on the inside cavity if they have been cracked or broken. This coating will exfoliate off at the slightest touch.
I have mostly worked with this material as hand specimen chunks. I have been unwilling to deliberately mash it to release the tektites. It is very friable and the tektites would be easily set free for individual examination. However, much of what this material has to teach is in the relationships of the spheres to each other and the matrix. Some of the large micro tektites are in fact collections of truly tiny tektites that have massed together but never welded. Others as mentioned before are hollow forms. Some whether through weathering or by their actual formation are vesicular with many voids and webs of glass inside them.
The material from Haiti has been linked to the Yucatan impact of the KT boundary. Their great age easily explaining all the devitrification which is seen. But, there are times in examining the material that you find areas where the micro tektites are still very glassy. In these cases you will see that the tektites have a greenish gray color.
Friable is often used to describe rocks that crumble easily. But, it is just not descriptive enough for the micro tektite material. This stuff falls apart from being looked at almost. You will dislodge enough micro tektites in normal positioning of the chunk for photography to keep you happy. I have only on a few occasions felt it necessary to pop out any glass spheres for more complete examination. Also, they are so brittle you run a great risk of them coming out incomplete when you try removing them from the soft matrix. They will fall out by themselves in sufficient numbers. Sort of like having a chunk of Saratov where no matter what you do you will have a few loose chondrules fall out.
One of my personal research projects has been collecting samples of ocean deposits from marine terraces near my home. It has been my hope to find some micro tektites mixed in these samples. The sampling continues, nothing to report, except I now have a vast collection of tiny fossil shells. I feared from the beginning of the project that I would not find micro tektites. Others far more qualified have had great difficulty finding micro tektites on land. But, it is a very interesting project I will continue as a rainy day activity.