Dr Brewster wi the Optical Analysis of Minerals. 15 
ing substances, whicb have been since found to be distinct mi- 
nerals, 
stilbtte. 
Heulandite. 
Brewsteirite. 
Stilbite from Aachen. 
Auvergne Mesotype. 
Scolezite or Iceland Mesotype. 
Thomsonite, or Kilpatrick Mesotype. 
Mesolite or Nadelstein from Faroe. 
Greenland Mesotype. 
Natrolite. 
Apophyllite Surcompose. 
TesseUte. 
Four of these crystals, viz. the Stilbite from Aachen^ the Green- 
land Mesotype^ the Tesselite., and the Nadelstein from Faroe., I 
found to be new minerals, from optical analysis alone ; and by 
the same method I have ascertained that all the other minerals 
above enumerated, are distinct mineral species. Hence we may 
conclude, that in every case where the chemical and crystallogra- 
phic methods have detected new mineral species, the method of 
optical analysis never fails to give the same result, and to trace 
in the variations of optical characters every change^of form or of 
composition. 
But, while this method must be regarded as superior to all 
other methods of discriminating minerals, as long as no instance 
(f failure can be pointed out ; it possesses at the same time an 
advantage to which neither chemical analysis nor crystallogra- 
phic dissection can aspire. It enables us to detect and explore 
those compound forms of dead matter which almost rival the 
organisations of animal life, and to study those Mosaics of the 
natural world which have entirely escaped the observation of 
mineralogists. I do not allude to those hemitrope crystalliza- 
tions which so frequently occur, but to compound structures 
which exist within regular geometrical forms,— which are cha- 
racteristic of the mineral in which they occur, — and which are 
essentially necessary to its existence. The most remarkable of 
these structures are the tesselated combinations of Apophyllite^ 
the aggregation of prisms which compose a perfect dodecahedral 
crystal of Sulphate of Potash^ the composite forms of Amethyst.^ 
Chabasite and Aplome^ and the still more remarkable assemblage 
of solids which constitute the Andlcime. 
It may be objected, however, to the optical method of ana- 
lysis, and with some semblance of justice, that its powers are 
