half as thick, the greater diameter being horizontal. The hole in these was quite small, and closed abruptly at the end. Fig.2 is peculiarly striking, and seems quite different in form from any yet described. These "bulbs" are said to correspond with the stratification in the sand.
Concerning the microscopic and chemical properties of the fulgurite, little seems to have been done until within a comparatively recent period. In 1875, Harting[1] examined some fulgurites found in acorn-field at Elspeet. He describes these as vitrified tubes, having a form scoriaceous, rough, and very irregular. Exteriorly they were coated with sand and carbonaceous particles, while interiorly they were of a white glass which was sometimes streaked with brown or black, a coloration which he judges to be due to distillation products from the vegetable matter in the sand. A complete chemical analysis of the fulgurite yielded results as follows: SiO2, 90,2 per cent; Al2O3, 0,9 per cent; Fe2O3, 0,7 per cent; CaO, 0,1 per cent; MgO, 0,5 per cent; K2O, 0,5 per cent; NaO, 0,6 per cent; insoluble in HCl, 0,9 per cent; carbonaceous matter, 5,6 per cent.
Discussing the results, the author argues that the alkalies and other bases, belonging to the vegetable matter, have been driven off by the heat of the flash, since the percentages shown are not greater than is contained by the sand itself. He also conceives that the presence of these bases may have aided in the reduction of the refractory silica—an idea which seems to have also been adopted by Gümbel and Wichmann. When, however, we consider the extraordinary brief duration of the flash and heat, this reaction seems scarcely possible.
Gümbel[2] describes fulgurites from the Libyan Desert between Dachel and the Ammon Oasis, in which the tube-wall consists of an amorphous glass enveloping un fused quartz-kernels. A partial chemical analysis led him to conclude the interior lining to be a true quartz glass. To this conclusion Wichmann[3] takes exceptions. This gentleman pulverized portions of the fulgurite tubes from Senner Heide, from Elspeet, and from Starczynow, and by means of a solution of great density[4] succeeded in separating the glass of the fulgurite from the inclosed sand. Chemical analysis of this yielded silica as follows:
| Senner Heide | 96·44 | per cent. |
| Elspeet | 94·26 | "" |
| Starczynow | 91·23 | "" |
- ↑ "Annales des Mines," vol. viii, 1875, p.700.
- ↑ "Zeit. der deutsch. geol. Gesell," vol. xxxv, p.648.
- ↑ "Zeit. der deutsch. geol. Gesell.," vol. xxxv, p.849.
- ↑ The solution in common use by lithologists, for separating finely powdered minerals of different specific gravities, is a saturated solution of the iodides of mercury and potassium. Properly prepared this can be brought to a density sufficient to float any substance of specific gravity not greater than 3,25. By gradually diluting the solution and thus rendering it less dense, it is possible to separate the various minerals of a powdered rock with a considerable degree of accuracy.
