MINERALOGICAL NOTES 
By J. REYNOLDS. 
Whilst the National Park affords great 
scope tor geniogicai workers, toe net a 
for the student of mineralogy is far 
more limited, but it is certainly not 
without points of interest. The brief 
stay at Easter afforded an excellent op¬ 
portunity for making detailed observa¬ 
tion, not only of the character but of the 
various decomposition products ofthe all 
predominating Mesozoic diabase. This 
well-known rock is composed ci r. mix¬ 
ture of two crystalline minerals, plagio- 
clase feldspar and a light coloured vari¬ 
ety of angite both highly siliceous min¬ 
erals. complicated In chemical composi¬ 
tion and crystalline habit. Occasion¬ 
ally the crystals are large enough to dis¬ 
cern with the naked eye, but none were 
observed, although some specimen* from 
“erratic" boulders near Lake Webster 
were coarse-grained. Near the top of 
Mount Field West a variety of more 
than usual interest is found. tiere Is 
an area in which the diabase has an¬ 
other constituent, namely, pyrite iron 
disulphide). This is one of the only 
known places where it is not barren of 
metallic mineral constituents for that is 
one o fthe peculiarities of diabase. The 
pyrite crystals (cubic) are brassy yellow, 
and are readily picked out with the 
naked eye. Undoubtedly it will be well 
worth carefully investigating this phen¬ 
omena more fully at some future date. 
The large scale demonstration of the 
power of glaciation as an agency in min¬ 
eral decomposition is not without In 
terest. Chemically speaking, diabase 
has the following approximate composi¬ 
tion:—Silica, 52 per cent.: lime. 12 per 
cent.; iron oxides. 8 per cent.; alumina, 
17 per cent.: magnesia. 6 per cent.; al¬ 
kalies, 3 per cent. Usually only the 
surface oi the diabase decomposes, and 
becomes covered with the remaining iron 
oxides, giving it the characteristic red 
dish brown colour, and protecting jt 
from further atmospheric action. Rut 
the glaciers which have come down the 
S3 road River valley, for example, have 
crushed trreat Quantities of diabase into 
a very line state, so that it has been 
readily acted upon by the quantities of 
water escaping from tlie milling gla¬ 
ciers. With a breaking up of the chemi¬ 
cal components of the mineral- we ge\ 
the following results—Firstly, the iron 
oxidises, and associates with the alumioa 
to form the clays of varying shades 
which are found in the Broad River vnl* 
ley. With them they take small amounts 
of the other constituents. Most of the 
silica and some of the lime is washed 
away owing to its lightness, forming 
sands further down the stream. Tne 
remainder of the lime together with most 
of the magnesia and alkalies are taken 
into solution by the water, and entirely 
removed from the locality. The two 
original minerals have been broken up, 
and the genesis of new minerals ha:s 
taken place. The highly ferruginous 
clay is gradually formed into one ot 
the iron oxide minerals—perhaps limoi.- 
ite, associated, of course, with alumlhj.. 
Transported lime and silica will eventu¬ 
ally go to build up new beds of lime¬ 
stone and sandstone, and so the cycle 
proceeds. Glaciation has greatly assist¬ 
ed these actions, both In speed and in 
scale, so it may readily be seen that as 
a natural agency it is of great import¬ 
ance, changing not only the topographical 
features but the state of mineral con¬ 
stituents in the zone of its action. 
HP Tl'P.Ai U V. .1 , 
