64 
RECORDS OF THE AUSTRALIAN MUSEUM. 
surfaces have a dull yellowish tinge deepening occasionally towards 
the edges. Internally they are colourless and translucent and 
shew the rhomboidal cleavage perfectly. 
In the one specimen the crystals of ankerite are associated with 
large and well formed crystals of quartz, some of which are left- 
handed, having both the rhombo- and trapezohedral surfaces. A 
few saddle-shaped crystals of siderite are deposited here and there 
on both minerals.* 
The other specimen contains no siderite, the associated minerals 
being quartz crystals, and a few large and numerous small crystals 
of albite. 
Normal ankerite has the formula 2 CaC0 3 . FeC0 3 .MgC0 3 
assigned to it and requires 
2 CaCO 3 
... 50-0 
FeCO 3 
... 29-0 
MgC0 3 
... 21-0 
100-0 
The analysis of the above mineral is seen to differ from this in 
the relative proportions of the carbonates of iron and magnesia. 
Calculated however for the formula 5 CaCO s .2 FeCO 3 . 3 MgCO s 
the percentages found agree exceedingly well with the theoretical 
Cal cu 1 ated . Found . 
5 CaCO, 50-81 50*76 
2 FeCO s 23-57 23-97 
3 JVIgCOg 25-61 25-93 
Borickyf writes the formula for ankerite and similar minerals 
thus : — 
(CaFeC g 0 6 ) + n (CaM gC , O 6 ), 
and states that n may vary from J to 10. When n is 1 the 
formula represents normal ankerite, but he assumes that those 
minerals in which n is 2 or less may be classed as ankerites, 
while he names those in which n is greater than 2 parankerites. 
The formula 5 CaCO 3 . 2 FeCO 3 . 3 MgC0 3 calculated for the present 
mineral may be written : — 
2 (CaFeC 3 0 6 ) -f 3 (OaMgC.O.) 
# These crystals of siderite have already been figured and described 
by the late Mr. F. Ratte in “ Notes from the Australian Museum,” Proc. 
Linn. Soc. N. S. Wales, x., 4, 1885, p. 759. 
f Boricky — Min. Mitth., xlvii., 1876. 
