10 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.60 



lar broken fragments. Such few crystals as were seen were much 

 rounded, with deeply striated and pitted faces, the forms being but 

 dimly distinguishable. 



MAGNETITE. 



Magnetite is much less abundant in the materials examined than it 

 is in black sands from most localities. In the lot from Camas County 

 magnetite in irregular grains and octahedral crystals is the most 

 abundant constituent, making up approximately four-fifths of the 

 whole, but this is the only example found in which magnetite is 

 present greatly in excess of ilmenite. The fine sands from the Snake 

 River contain varying amounts of black iron ore up to about 30 per 

 cent. This is in large part in irregular dull-black grains and it is 

 not possible to determine in what part these grains are magnetite. 

 About one-half of the total amount of black material is removed by a 

 magnet. When this magnetic portion is examined it is found to con- 

 sist mainly of rough irregular grains with occasionally a brilliant 

 black tabular crystal of ilmenite. Other crystals of ilmenite are non- 

 magnetic. Rarely the magnetic material shows octahedral crystals 

 of magnetite. Magnetite is present in negligible amount in the many 

 monazite-bearing sands of the Boise Basin and of the Pierce City 

 region, the black mineral being almost entirely ilmenite, which in 

 these sands is not attracted to a magnet. Where the magnetite is in 

 distinct crystals, it is in the form of octahedrons, which may be more 

 or less distorted. In some coarse sands the magnetite is in small fine 

 granular masses and in rare cases this mineral forms pseudomorphs 

 after well defined pyrite crystals. 



ZIRCON. 



One of the most interesting and widespread constituents of the 

 heavy sands is zircon, which occurs in greater or less amount in every 

 sand examined. Ordinarily the mineral is clear and colorless, and 

 it is invariably in beautifully sharp crystals, most of which are very 

 transparent and brilliant. It occurs in considerable amount in the 

 sands from the gold placers of the Boise Basin, where it is associated 

 with monazite, but it is still more abundant, according to Lindgren,* 

 m some placer districts, notably those near Florence and Wan-em 

 where the heavy residues are called " white sand " because of its pres- 

 ence. While commonly colorless, the zircon in the sands of the 

 granite region varies from smoky gray to pale flesh red. The smoky 

 crystals are much like smoky quartz in appearance and the color 

 Is often unevenly distributed. Inclusions are frequent, the most 

 highly transparent and brilliant forms containing minute spherical 



•Undgren, Waldemar, D. S. Geol. Survey, 20th Ann. Kept., pt. 3, p. 234, 1899. 



