Tektites of Coco Grove

Title

Language

English

Year

1939

Rights

In Copyright - Educational Use Permitted

Fulltext

TEKTITES OF COCO GROVE (PART II) By D. VAN EEK DESCRIPTION The tektites of Coco Grove have a fresh appearance and some of them show very tiny protuberances. Many specimens are broken by rolling through the iron screen, they can not have been transported. Consequently, they must be lying in the same place where they fell. Nearly all of them show a flat or slightly round bottom side, presumably the side they fell upon. The flat bottom side shows the typical chicken skin pitting but in most cases no grooves; the upper side shows grooves as well as pitting. Sometimes larger holes are seen on the surface but these can be considered as only a coar ser pitting. Queer curves and spiral lines are sometimes shown on the sur face; these are considered to be fluxion lines. CAUSE OF THE LINES OF FLUXION When a meteorite (or tektite) enters the earth atmosphere with a cosmic speed of ca. 100 km. per second (62 miles per second) its temperature of the skin and interior is raised due to friction with the air. Only the surface temperatures can reach a very high temperature ca. 1500° C) and can be come fluid, and commence to give off light at ca. 150 km. above the earth’s surface. The high temperature penet rates only about 1 mm. into the body and the interior rises only very slowly in temperature. Consequently the larger the body, the cooler the center; on its way toward the earth the fluid material flows over the surface and is wiped off forming the fiery tail of the meteorites (or tektites) and drawing lines on its surface, the fluxion lines, which can form queer spirals due to the rotation. CAUSE OF THE SURFACE PITTING The chicken-skin pitting has been caused probably by rapid cooling. It has been believed by some authorities that the pitting is caused by small pieces being broken off the surface by friction of the air, causing the chicken skin pitting and larger holes. But the latter is impossible for pitting is also found on broken fragments. CAUSE OF THE GROOVES The grooves are also considered by some to be caused by etching and have been produced artificially by fluoric acid on a fresh tektite surface. But examination of the larger specimens showing clear and regular grooves show that the grooves are cracks probably caused by the shock when the tektite hits the earth surface. Before they reached the ground tektites assume a sphere (or drop) form. We consider a sphere of a homogene substance drop ped down just as a tennis-ball drop upon an unyielding surface, the sphere will transform itself to an oval as soon as it hits the ground. But as silica glrss is nonelastic as a tennis-ball, it will soon be impossible for it to transform any further and then it will break; cracks will appear in two systems. One system of crack will be perpendicular to the direction of the largest expansion (extension), these are called tension cracks. The other system will occur at an angle to the direction of the largest contraction (pressure) ; these are called shear cracks. Other geologists consider that the pitting is caused by etching with fluoric acid which might be present in the ground water. In the mines near Coco Grove no fluor-minerals are known to occur, consequently there will be no fluoric acid in the ground water and a stronger reason is that clear trans parent quartz crystals are found in the same sands containing tektites. Those crystals are not etched. Why should the silica of the tektites have been etched and the silica of the quartz re main unaffected? The Marsman Magazine for September, 1939 Cross - Glctiom Of Coco Shove. METHOD OF OPENING CRACKS In most instances, the bottom of the grooves is found covered with some red dish material which simulates burned clay, consequently, the tektites might have fallen at a time when the entire Coco Grove property was covered with sea, marsh, or mud flat, on the bottom of which the clay was lying. Con sidering that the tektites were falling into the water or marshy land, the sur face layer would be cooled off more slowly and retained a greater plasticity. Therefore, the surface layer reached first the stage of cracking while the in side kernel (containing a gas-hole) could transform itself still further with out cracking and tore the cracked pieces of the surface layer out of each and opened up the cracks. That those cracks have been torn apart is still The Marsman Magazine for September, 1939 shown by tiny striations on the bottom of the grooves. Sometimes the surface layer will break off and we find fragments. The larger tektites were more often af fected in this manner. These fragments also show striations. The smaller tektites, that is, those lighter than 80 grams, do riot show shear cracks but in most instances ten sion cracks appear. Below 30 grams they generally possess a slaggy appear ance. The white material sometimes found in the grooves is decomposed granitic material from the bedrock. According to previous examinations changes in temperature will cause scant contraction or expansion of these silicates, therefore, the grooves are not the result of cooling. (As no laboratory work has been done, it has not been proven here). 11 THE AGE OF THE TEKTITES— PLEISTOCENE — OR RECENT? Shells found in the pay dirt are simi lar to those which are found on the beach, as far as can be roughly judged. A careful study by an authority on shell forms might date them more ex actly. The entire complex of layers may be formed in ca. 20,000 years or less if no layers are missing. If a thorough microscopic investigation should be made of the sand, the exact stratigraphic horizon where the tek tites dropped might be found as that place might be marked by large quanti ties of tiny tektite fragments and prob ably by changes or burning of the layer. If that is known, a calculation of the age of the covering layers will give the age of the tektites. At least 10,000 years ago the Stone Age people used them as charm stones and made imple ments of them such as arrow heads, scrappers, etc. USE—PRACTICAL APPLICATION The gold panners of Paracale have known for hundreds of years that tek tites were characteristic of the sands carrying the largest quantity of gold and consequently they called tektites the Mother of the Gold. As tektite must have been falling shortly (geolo gically speaking) after the deposition of the pay dirt, they may be useful also in other regions to mark the gold bear ing sands.—In addition many Univer sity museums are interested in these tektites, and it would be a form of ad vertisement if Coco Grove Inc. would present some nice specimens as a gift. Besides marking the pay dirt in Paracale Basin and thus providing a readily visible marker, they maybe use ful for correlation purposes, assuming a single fall. In addition, they possess scientific interest as possible represent atives of fragments from a source out side of the hemisphere, and consequent ly having some bearing on earth his tory and the composition of original material of the earth. As they possess scientific value, a collection of tektites might be saleable to scientific institu tions or to other interested persons. A. F. Kelly, treasurer of the Marsman-managed companies, and of Marsman & Company, left September 21, on the President Coolidge for San Fran cisco where he will be temporarily at tached to Marsman company of Califor nia at San Francisco. Mr. Kelly joined the staff of the com pany in November 1931. Prior to his engagement with the Marsman enter prises, Kelly had wide and varied expe rience in finance and banking. A great part of the intricate mine-accounting system used in Marsman operations is the result of his work and instigation. 12 The Marsman Magazine for September, 1939

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