Vol. 5] 



LouderbacTc. — Benitoite. 



379 



in either set. The measurements therefore indicate orthorhombic 

 symmetry. 



The pyramid faces which in a mineral of so simple a habit 

 as is here shown would be expected to have rather simple indices, 

 give approximations to only very complicated titanite forms. 

 The nearest simple possible titanite forms are (221) and (344) with 

 jA(221)=70° 37', zA(334)=76° 37' the measured value being 

 76° 37'. The coincidence of the last figures is shown to have no 

 meaning, as <£ 4 -</> :1 referred to x as pole is 79° 15' in titanite, 

 85° 9' measured. A closer approximation would be (354) and 

 (T7 13 8). As regards the form called a above, the nearest 

 approximation, with simple index, is titanite (T01) where 

 ./ A (101) is 86° 56', measured 89° 42' orthorhombic should be 

 90° 00'. A closer titanite approximation would be (17 16). 



The attempt to make this crystal combination a habit of 

 titanite is not successful and leads to very improbable results, 

 while all of its properties so far determined consistently fit into 

 the orthorhombic scheme. It may be noted here that under the 

 microscope its most marked divergence from titanite is its in- 

 ferior cleavage and straight extinction wherever cleavage cracks 

 are observable. 



This mineral may contain some other elements not shown in 

 the preliminary microehemical tests, but it may also be a di- 

 morphous form of titanite, or an orthorhombic end member of an 

 isomorphous series. 



The name is taken from the ridge (primarily anticlinal com- 

 ponent) of the Diablo range on which the mineral occurs. The 

 ridge received its name from the prominent Joaquin rocks — a 

 landmark of the region. 3 " It also borders the great San Joaquin 

 valley. 



Joaquinite is found enclosed in the natrolite, both at the edge 

 of the veinlets and touching the wall rock, and also in the central 

 portion of the vein. It is also found enclosed in the neptunite 

 and seems especially to occur in those parts of the deposit rich 

 in neptunite. Both the natrolite and neptunite are molded about 

 it xenomorphically. 



so See further Arnold and Anderson, Bull. U. S. Geol. Survey, No. 357 

 ( 1908), 13. 



