358 
Proceedings of the Royal Society of Edinburgh. [Sess. 
material is so abundant that it promised to be of “ high economic import- 
ance.” * The material was massive, and no crystals were found ; its 
composition, according to Professor Louis’ three analyses, is — 
Calcium carbonate 
... . 1-92 
Ferrous „ 
. 68-15 
Manganous „ 
1-87 
Magnesium ,. 
. 28-06 
100-00 
Excluding the carbonates of calcium and manganese as accidental 
impurities, Professor Louis calculated the essential constituents as 
Ferrous carbonate ..... 70-02 
Magnesia „ ..... 29"98 
and the formula as 5FeC0 3 + 3MgC0 3 . Professor Louis maintained that 
owing to the large quantities of this material the sideroplesite should “ be 
classed as a well-defined mineral species rather than as a mere variety of 
siderite.” *f* 
Heddle has recorded J sideroplesite from Scotland ; he found it in the 
deeper parts of the Sandlodge mines on the eastern coast of Shetland, south 
of Lerwick, where 
it occurs in quartz associated 
with chalcopyrite. 
Heddle regarded it 
as a calcareous variety of mesitite 
or pistomesitite, of 
which the composition is as follows 
. . i 
r MgCOo 
. 59-2 
Mesitite -< 
) & 3 
l FeCO s 
. 40-8 
Pistomesitite j 
: MgCOo 
. 42-0 
1 & 6 
L FeC0 3 
. 58-0 
Heddle’s analysis of the mineral from the Sandlodge 
it contained 
mines showed that 
Carbonate of iron ..... 
. 62-4 
„ manganese 
. 20 
?? 
„ magnesia .... 
. 24-9 
„ lime . . 
. 9-9 
Silica 
•8 
1000 
His material, therefore, is not a typical sideroplesite, as the proportion of 
the siderite molecule is too low. 
* Ibid., p. 50. t Ibid., p. 52. 
J M. F. Heddle, Mineralogy of Scotland, vol. i., 1901, p. 141. 
