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Proceedings of Royal Society of Edindourglfi, [july 16, 
transparent, they exhibited now more of a yellowish-green tint, 
and their diaphaneity was rather translucent than transparent. 
Their hardness was also reduced to about 6 *5. 
I noticed also that crystals naturally aggregated together, when 
put into the water, tended to separate from one another after a 
month or two’s exposure to the carbonated liquid. 
Being curious to learn the effects of the action of the carbonic 
acid water on the microscopic character of olivine, I got two 
specimens sliced, one of which was a fresh crystal, and the other a 
crystal originally identical with the former, hut which had lain for 
two months immersed in the carbonated fluid. Fig. 1 shows the 
fresh specimen as observed under the microscope, and fig. 2 shows 
the same variety of mineral after its two months’ treatment. 
Fig. 1. — Afresh Crystal of Olivine. Fig, 2. — A Crystal of Olivine which 
a a, fissures. Magnified about had been subjected to two 
60 diameters. months’ immersion in water 
saturated with Carbonic Acid 
Gas. a a, fissures. Magnified 
about 60 diameters. 
In the unaltered crystal (fig. 1) the irregularly distributed cracks 
are much finer than those shown in the altered crystal in fig. 2, 
where they have evidently been widened considerably by the solvent 
action of the carbonic acid water. 
In fig. 2 there is also a very distinct serpentinous formation 
about the cracks of the mineral, which is only very slightly 
developed in the fresh specimen, and in addition several faint red 
spots or patches of ferric oxide can be observed on the edges of the 
fissures ; these are wholly wanting in the fresh crystal figured 
(fig- 1)- 
I have noticed also, that whereas in the freshest olivine neither 
of the cleavages are visible, or if visible not at all weU marked, in 
