230 Field Columbian Museum — Geology, Vol. i. 



similar to those previously described. The color of the crystals of 

 all types varies from a pale yellow to a deep orange. Some are per- 

 fectly transparent, but the majority are translucent to opaque. The 

 yellow color is probably due to the presence of iron, as on heating 

 the crystals turn black and become slightly magnetic. Other quali- 

 tative tests likewise indicate the presence of considerable iron. 



DOLOMITE USED AS INDIAN MONEY. 



NEAR LAKEPORT, LAKE COUNTY, CALIFORNIA. MUSEUM No. M6387. 



Specimens of dolomite from the above locality, and of the 

 " money " made from it, were collected by Dr. G. A. Dorsey, Curator 

 of Anthropology of the Museum, during a visit made in 1889 to the 

 Porno Indians, a tribe of the Kulanapan stock who inhabit the region. 

 The material has long been used as a medium of exchange among 

 these Indians, but I cannot learn that it has been hitherto described. 



The mineral occurs in the form of nodules, or boulders, roughly 

 oval in shape, and from four to eight inches in diameter. They are of 

 ■ a rusty yellow color upon the surface and the local Indian name for 

 them, Pol' -ka-be, means rusty color. A freshly fractured surface 

 shows a pure white color, except for occasional rusty seams, and 

 lustre like that of unglazed porcelain. The texture is compact an,d 

 fracture flat conchoidal. A determination of the specific gravity of a 

 pure white fragment gave G. = 2.878. Dr. Dorsey did not visit the 

 mine whence the dolomite is obtained, but was informed that it was 

 situated on the east shore of Clear Lake, a few miles southeast of 

 Lakeport. 



While the mode of occurrence cannot be stated with certainty, 

 it is probable that it is as residual boulders in a reddish clay. 



A partial analysis by the writer gave Ca O, 28.27%, Mg O, 

 22.46%, and Fe O, 1.18%. These percentages are nearly those of 

 a typical dolomite. 



The use of the mineral by the Indians as a medium of exchange 

 is a long established custom, and the value at which they esteem a 

 well worked piece is nearly equal to its weight in gold. In order to 

 make the money, symmetrically shaped cylindrical pieces are cut out 

 from the crude boulders. These are burned and the burning brings 

 out reddish streaks of color doubtless from oxidation of the iron, 



