554 DK. r. H. HATCH 02f THE SPHEKOID-BEARING 



In order to determine the nature of the felspar and of the black 

 opaqne mineral, a portion of the spheroid was detached and, after 

 being freed from its outer coating of orthoclase, crushed in a steel 

 mortar. From the powder small fragments of about 1 cubic miUim. 

 were sifted out, and of these a few selected which were as free as 

 possible from the opaque inclusions. Tested for their flame-reactions 

 by Szabo's method, these fragments ga^e results indicating a lime- 

 soda-felspar of intermediate composition. The fusibility, on Szabo's 

 scale, is 4. 



The fragments were now farther crushed until the whole powder 

 was sufficiently fine-grained to pass through a piece of fine cambric, 

 stretched across the mouth of a beaker to serve as a sieve. On 

 going over the powder carefully with a small bar-magnet, the black 

 opaque granules were easily removed, and were found to be com- 

 pletely soluble in hot hydrochloric acid. These are properties of 

 magnetic iron-ore. The total weight of the powder was 3-07 grm., 

 that of the magnetite removed '37 grm., or 12-1 "/q. 



The remaining powder was then introduced into aSonstadt's solu- 

 tion of such strength that in it calcite (sp. gr. 2-715) just remained 

 suspended. On standing, a dark powder separated, and was 

 removed. This, examined under the microscope, was found to con- 

 sist mainly of biotite, but mixed with fragments of felspar (rendered 

 specifically heavier by minute inclusions of magnetite) and a small 

 quantity of isolated magnetite. 



The solution was then carefully diluted until the remaining powder 

 (felspar) appeared neither to sink nor to rise. The specific gravity 

 of this solution, taken at 15° C. by means of a Westphal's balance, 

 was 2*649. This is almost identical with the result obtained for 

 the specific gravity of the plagioclase of the surrounding granite 

 (vide at supra). In a solution in which orthoclase (of sp. g. 2-571) 

 floated, the whole powder sank to the bottom, proving conclusively 

 that no orthoclase is present in the zonal portion of the spheroid. 



A chemical analysis of this powder gave the following results : — 



SiO, 60-99 



Al^Og (with a little Fe^Og) 25-56 



CaO 4-88 



I^a.O* 7-73 



Loss on ignition '84 



100-00 



* By difference. 



This agrees very nearly with the theoretical composition of an 

 oligoclase of the formula AbgAn^ f. 



To sum up shortly these results, we find that the spheroids con- 

 sist of two parts : — a pinkish central portion (the nucleus) and a 



t Oligocla&e of the formula Ab3 An^ has the following composition : — 

 Si,0=61-9; Al203 = 24-2; CaO=52; Na^O^S-?. Tschermak, I.e. 



