Show simple item record

A Stony Meteorite From Forksville, Mecklenburg County VirginiaShow simple item record

dc.creatorMerrill, George P. (George Perkins), 1854-1929
dc.date.accessioned2024-02-12T18:11:37Z
dc.date.available2024-02-12T18:11:37Z
dc.date.issued1927
dc.identifier.urihttps://repository.tcu.edu/handle/116099117/63201
dc.descriptionArticle covering the Forksville, Virginia meteorite by George P. Merrill, head curator of Geology at the United States National Museum.
dc.relationOscar Monnig Papers (MS 124)
dc.rightsPrior written permission from TCU Special Collections required to use any document or photograph.
dc.sourceSeries III, Box 06, Forksville folder
dc.subjectMeteorite
dc.subjectForksville meteorite
dc.subjectForksville (Va.)
dc.subjectSmithsonian Institution
dc.subjectMetallography
dc.subjectMerrill, George P.
dc.titleA Stony Meteorite From Forksville, Mecklenburg County Virginia
dc.typeArticle
dc.description.transcriptionA STONY METEORITE FROM FORKSVILLE, MECKLENBURG COUNTY, VIRGINIA By GEORGE P. MERRILL Head Curator of Geology, United States National Museum The data concerning the fall of the stones here described were gathered by the late Dr. Thomas L. Watson, of Charlottesville, Va. Three of the four stones which, so far as known, comprised the entire fall, were secured by Doctor Watson at the time and brought by him to Washington for consultation with the present writer, with a resultant agreement to the effect that the chemical analyses, sections, and other essential cuttings should be done here while the microscopic studies should be his. The fourth and largest individual, secured later, was found among Doctor Watson's effects after his death. According to Doctor Watson's notes, the fall took place within the town of Forksville, Mecklenburg County, in southern Virginia, on the afternoon of July 16, 1924, between the hours of five and six but nearer the last-mentioned hour. The stone was traveling in a northwest to southeast direction and was accompanied by the usual artillery-like explosions; the noise lasted four or five minutes but no light accompanied it--this doubtless due to the time of day. The record of the four stones as given is as follows: No. 1, weight 2,250 grams, fell about half way between Brodnax and Forksville on R. D. Temple's place; is reported to have been entirely cold when recovered some 15 minutes after the fall. No. 2, weight 1,850 grams, struck within some 450 feet of a woman who heard the explosion apparently directly overhead; it made a hole inclined at 10 degrees from the vertical, some 6 inches in diameter, and 18 inches deep in the soft mud. No. 3, weight 853 grams, fell in an open field on Mrs. Trutter's place, making a hole some 4 inches to 6 inches wide and 6 to 8 inches deep. No. 4, weight 1,114 grams, fell near a colored burial ground near the Seaboard Airline Railroad tracks and was seen by 50 to 75 colored people. The appearance of the four individuals is shown in Plates 1, 2, and 3. No. 1 shows both primary and secondary encrustation; No. 2 is evenly encrusted excepting where broken away in striking; Nos. 3 and 4 (pl. 3) are both well encrusted, but 4 shows a secondary crust on the upper surface, not shown in the figures. The texture is quite uniform and plainly chondritic. The individual shown in Figure 1, Plate 3, was cut in halves and from the central portion was selected the material for analysis and sections. In the thin section the stone shows a structure and composition common to those of its class--a confused, often obscure tuffaceous ground carrying indistinct chondritic forms of both olivine and pyroxene, as a rule not sharply differentiated from the ground but showing irregular and finely granulated borders due to crushing and of the nature that has given rise to the supposition by some -that the apparent tuffaceous nature of chondritic stones is really cataclastic through shock or compression. The pyroxenes give, in most cases, extinctions parallel to the vertical axes; occasional larger forms have extinction angles as high as 12 to 15 degrees, and hence are assumed to be clinoenstatite. Rarely occurs a small, irregular, colorless area without cleavage lines which might readily be assumed to be an undifferentiated residual glass but that it polarizes in light and dark colors and is therefore considered a maskelynite. That merrillite or apatite--or both--is present is indicated by a phosphoric-acid test but neither mineral was recognized microscopically. No trace of oldhamite or other unusual minerals could be detected. The stone shows a rusty black, lusterless crust and on a freshly broken surface is of an ash-gray color which quickly becomes covered with rusted spots. Dark chondrules ranging in sizes in one instance up to five millimeters are abundant as are also small flakes of metal. As a rule the chondrules break free from the matrix. I have classed the stone as a spherulitic chondrite (Cc). The results of chemical investigation by Earl V. Shannon are given below. The composition of the whole stone is as follows: […] Concerning the methods employed in these analyses, Mr. Shannon says: Fragments of the stone, free from crust, to the weight of 32 grams, were ground to pass a 12-mesh screen. This sample was thoroughly mixed and a 5-gram portion was ground to pass 80 mesh, and all magnetic particles were removed from it by repeatedly working over the sample with a hand magnet. This metallic portion was digested in a hot solution, saturated, of mercuric chloride, whereupon the metal went into solution. The undissolved silicate was filtered out and weighed. The solution, after being freed from mercury, was analyzed by the standard methods, giving the composition of the metallic portion. The silicates were thoroughly mixed and a 2-gram portion weighed into a casserole, covered with 200 c. c. of 1: 1 hydrochloric acid and evaporated to dryness on the steam bath. The residue was then moistened with a mixture of nitric and hydrochloric acids to decompose any cohenite or schreibersite, again evaporated to dryness, taken up in hydrochloric acid and filtered. The residue, after thorough washing with hot water, was digested on the steam bath with 10 per cent sodium carbonate solution. This was again filtered and washed with hot water until free from alkali, then rinsed once with hydrochloric acid and washed free from acid. The acid and alkali extracts were united, evaporated to dryness, and analyzed by standard methods, giving the composition of the soluble silicate portion. The residue on the filter was weighed as insoluble silicate and analyzed by standard methods to give the composition of the insoluble silicate. Sulphur was determined by the standard method in a separate portion and assigned to the soluble portion. Alkalies were determined on another separate sample of the powder and relegated to the insoluble silicate. The results of the analyses as given above are fairly typical for stones of the class. So far as relative proportion of metal and silicates, and composition of the metal are concerned, the results are in close agreement with those obtained by Whitfield on the stone of Elm Creek, Kans.2 The metal content, it will be observed, is below the average (11.98%) of stony meteorites as given in the paper quoted. The ratio of metal to nickel is about 7 to 1, and that of magnesia (MO) to ferrous oxide (FeO) in the magnesium silicates but 1 to 1. These facts are of interest in connection with generalizations that have been made on the subject.3 EXPLANATION OF PLATES PLATE 1 Two views of the largest individual. Actual size about 13 by 10 by 9.5 cm weight, 2,250 grams. Shows primary and secondary encrustation. PLATE 2 Two views of second largest stone. Actual size, 13 by 7 by 7 em.; weight, 1,850 grams. PLATE 3 The two smaller stones. Fig. 1: Size, 7 by 10 by 0 cm.; weight, 1,114 grams. Fig. 2: Size, 7 by 9 by 6 em.; weight, 850 grams. Forksville, Virginia, Meteorite For explanation of plate see page 4 Forksville, Virginia, Meteorite For explanation of plate see page 4 Forksville, Virginia, Meteorite For explanation of plate see page 4


Files in this item

Thumbnail
Name:
Forksville_001.pdf
Size:
128.6Mb
Format:
PDF

View/Open

This item appears in the following Collection(s)
  • Records of the Monnig Meteorite Gallery [2825]
    The files are arranged alphabetically, usually according to the location of discovery of the meteorite. The files contain correspondence and research material on the meteorites in the collection.

Show simple item record

© TCU Library 2015 | Contact Special Collections |