CONTRIBUTIONS TO MICRO-MINERALOGY. 223 



better than regarding these different states, as some authors 

 have done, as grounds for Specific distinctions. 



As crystallization gives individuality to the Mineral mass, 

 the Crystal System should be the ground for determining 

 Specific distinctions. 



From considerations of the allotropic condition of matter 

 in dimorphous bodies, probably each crystal form has an 

 amorphous state of its constituent peculiar to itself. Thus 

 Rhombic Sulphur is produced from solution at low tem- 

 perature, and has an amorphous state common to it at ordi- 

 nary temperatures. MoNOCLiNic Sulphur, on the other 

 hand, exists only at high temperatures, and there is an allo- 

 tropic amorphous state of sulphur that, likewise, exists only 

 at high temperatures. 



Ordinary honey-coloured amorphous Phosphorus produces 

 from solution Rhombic Dodecahedrons ; probably the black 

 amorphous phosphorus would produce, under favouring cir- 

 cumstances, crystals belonging to a different system. Several 

 other instances might be cited, but it would be out of place 

 to enter further on this part of the subject in the pages of this 

 Journal, and 1 therefore proceed to the consideration of the 

 objects more specially in view. 



It is my intention to consider the subjects of these contri- 

 butions under the following heads or parts : — 



1st. The Instruments of Micro-Mineralogical re- 

 search. 



2nd. Micro-Crystallography. — Under this head I purport 

 describing crystal forms as seen in the field of the 

 Microscope, — Goniometry. — The means of determin- 

 ing true forms from apparent forms, caused by optical 

 and other deceptions. The Crystal-Systems under 

 which microscopical crystals may be classed. The 

 relation of Polarized light to the different Crystal- 

 Systems, and the method of measuring the angles of the 

 optic axes, diameter of the rings, and amount of 

 rotation, &c. in depolarizing crystals and inorganic 

 bodies, and the method of determining the Crystal- 

 System to which a crystal belongs, by means of 

 Kobell's Stauroscope. The relation that exists between 

 the symmetrical grouping of crystals and the Crystal- 

 System to which they belong ;* and here a new field for 

 inquiry is open. In Vol. III. of this Journal, Plates 

 XIII. XIV., are figured many very beautiful groupings 



* I drew attention to tliis subject in No. I. of 'The Chemist,' New 

 f?eries, p. 58 ; 1853. 



