354 Palmer — Arizonite, Ferric Metatitanate. 



be measured only approximately with a hand goniometer and 

 with a probable error of several degrees. So far as could be 

 determined from the forms present, the crystal system is prob- 

 ably monoclinic, in which case the plane of projection of fig-. 

 1 is the plane of symmetry and the indices of the different 

 faces are a (001), 6(100), c(101), rf(001), e (110) and /(Il2). 

 Between these faces the following angles were measured: 



Reflection. 

 001:100 = 125° fair 100:0.01= 51° poor 



fair 



100 



:0,01 = 51° 



a 



100: 



: 112 = 90° 



poor 



110: 



101 = 117° 



a 



110 



: 112 = 130° 



a 



101 : 



: 001 = 110° 



a 



112 : 



: 101 = 124° 



001 : 101 = 80° -. 



001 : 112 = 60° 



100 : 110 = 123°.. .. 

 100 :101 = 130° 



These values are not sufficiently accurate for a satisfactory 

 determination of the axial ratios, but it is approximately 

 a:l:c = 1*88:1 : 2-37; j3 = 125°. 



In the above calculation of the axial ratios, it is assumed 

 that the plane of projection in fig. 1 is a plane of symmetry. 

 No proof of this, however, was obtained, and it is possible that 

 the crystal system is triclinic or other system instead of mono- 

 clinic. Etch figures would be of service in deciding definitely 

 the system from the single crystal available. 



" tinder the microscope the larger particles of even fine 

 powder are opaque, but the very thin edges of minute slivers 

 are deep red in transmitted light, highly refracting {n > 1*84) 

 and of medium birefringence. Pleochroism is barely notice- 

 able in shades of deep red with absorption r > a- In the 

 thin section noticeable amounts, about 4 per cent or less even 

 in the freshest material, of a colorless to pale brownish yellow, 

 highly refracting substance, uniaxial and optically "negative, 

 occurs and agrees in its optic properties with anatase. 



" A thin section made from an alteration product of the new 

 mineral shows that, as the alteration of the latter proceeds, the 

 amount of the anatase present increases until finally practi- 

 cally the entire substance is changed to a mesh work of fine 

 anatase aggregates. The luster becomes dull and lithoid, and 

 the color changes gradually from dark steel grey to a brown- 

 ish yellow. In the freshest material there is also present in 

 minute grains and laths a colorless, strongly refracting and 

 birefracting mineral which is not anatase but is negligible in 

 amount, and, so far as its effect on the chemical analysis of this 

 material is concerned may be disregarded." 



The mineral is decomposed completely by hot concentrated 

 sulphuric acid. The residue, insoluble in the sulphuric acid, 

 contained all of the silica and about one half of one per cent 



