286 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



systematic collections arranged according to the generally accepted 

 classification. Among the stony irons (Pallasites) attention may be 

 called to that from Mount Vernon, Ky., and of the stones, the coarse 

 breccia from Cumberland Falls in the same State and to the chon- 

 dritic types from Allegan, Mich., and New Concord, Ohio. 2 



In the introductory cases are included also examples of the so- 

 called tektites (billitonites, australites, moldavites, etc.) considered 

 by some as of probably meteoric origin. 



THE GRANITE PEGMATITES AND THEIR ASSOCIATED MINERALS. 



The peculiar structural phase of granite known as pegmatite or 

 sometimes graphic granite, is of both great scientific and economic 

 interest on account of the minerals it carries, either accessory or as 

 essential constituents. The two essential constituents, feldspar and 

 mica, are of greatest economic importance. The accessory gem 

 minerals are beryls and tourmalines, but numerous other interest- 

 ing forms occur making the pegmatites a favorite hunting ground for 

 the mineral collector. The collections exhibited are designed to show 

 their general character and mineral associations. 



The eastern pegmatites, and particularly those of Maine, are noted 

 for their green tourmalines, aquamarines, and blue apatites. The Cali- 

 i'ornian pegmatites owe their great popular interest to the two gem 

 minerals, kunzite and pink tourmaline. These occur in pockets or 

 cavities, filled with other fragmental and decomposed material. As 

 arranged a quantity of clastic material is shown as taken from the 

 ground, and then the same amount separated into its component 

 parts, of quartz fragments, feldspar, kunzite, tourmaline, etc. Both 

 of these collections are described in detail in the catalogue of the 

 Isaac Lea collections of gems and precious stones (Bull. 118, U. S. 

 N. M.) and need no further consideration here. 



MISCELLANEOUS AND MINOR EXHIBITS. 



Imitative forms. — The forms assumed by inorganic matter some- 

 times so closely resemble those that are organic or of artificial 

 origin as to be quite misleading, or at least create a feeling of doubt 

 in the minds of those who have not given the subject special atten- 

 tion. The collection here brought together is designed to show some 

 of these forms and to explain, so far as possible, their true nature. 

 The dentritic deposits of manganese oxide so often mistaken for 

 " fossil moss " and ferns, vesicular furnace slag supposed to be wasp 

 nests, the coral thought to be honeycomb, and other more or less 

 imitative forms are here shown. 



2 For details of this collection, up to date of publication, see Bull. 94, U. S. Nat. 

 Museum, 1916. 



