424 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 59. 



These figures compare well with those of Wells's as given below, 

 recalculated to conform with method of statement used by Wells. 



Analyses of creedite. 



Larsen and Wells write the formula for creedite as CaSO,. 2CaF, 

 2A1(0H) 3 . 2H 2 0. It may also be written 3CaF 2 . Al(OH,F) 2 SO,l 

 2H 2 0. A determination of the water at various temperatures showed 

 a loss of only 0.08 per cent at 250°. However, if we consider the 

 water as all constitutional it becomes difficult to assign a simple 

 formula to the mineral. 



RELATIONS. 



Creedite does not appear to be very closely related to any known 

 mineral. Since it is predominately a fluoride it is best classed with 

 them. Ainong these it stands closest to pachnolite with two mole- 

 cules of sodium fluoride replaced by one of calcium sulphate. Its 

 apparent relationship can be brought out by doubling the formula 

 for pachnolite : 



Pachnolite 2CaF,, 2A1F 3 , 2H 2 0, 2NaF. 



Creedite 2CaF 2 , 2A1 (OH,F) 3 , 2H 2 0, CaSO,. 



Creedite can then be grouped with pachnolite in a systematic 

 classification until some closer relations can be shown. 



