They are distinguished in substance of parts and the accidents thereof, that is, in colour and figure; for Ice is a similary body, and homogeneous concretion, whose material is properly water, and but accidentally exceeding the simplicity of that element. But the body of Crystal is mixed; its ingredients many, and sensibly containeth those principles into which mixt bodies are reduced. For beside the spirit and mercurial principle it containeth a sulphur or inflamable part, and that in no small quantity; for besides its Electrick attraction, which is made by a sulphureous effluvium, it will strike fire upon percussion like many other stones, and upon collision with Steel actively send forth its sparks, not much inferiourly unto a flint. Now such bodies as strike fire have sulphureous or ignitible parts within them, and those strike best, which abound most in them. For these scintillations are not the accension of the air, upon the collision of two hard bodies, but rather the inflamable effluencies or vitrified sparks discharged from the bodies collided. For Diamonds, Marbles, Heliotropes and Agaths, though hard bodies, will not readily strike fire with a steel, much less with one another: Nor a Flint so readily with a Steel, if they both be very wet, for then the sparks are sometimes quenched in their eruption. [Sidenote: _The Physical causes of liquation or melting of Mettals, etc._] It containeth also a salt, and that in some plenty, which may occasion its fragility, as is also observable in Coral. This by the Art of Chymistry is separable, unto the operations whereof it is liable, with other concretions, as calcination, reverberation, sublimation, distillation: And in the preparation of Crystal, _Paracelsus_ [SN: _de Præparationibus._] hath made a rule for that of Gemms. Briefly, it consisteth of parts so far from an Icie dissolution, that powerful menstruums are made for its emollition; whereby it may receive the tincture of Minerals, and so resemble Gemms, as _Boetius_ hath declared in the distillation of Urine; spirits of Wine and Turpentine; and is not only triturable, and reducible into powder, by contrition, but will subsist in a violent fire, and endure a vitrification. Whereby are testified its earthly and fixed parts. For vitrification is the last work of fire, and a fusion of the Salt and Earth, which are the fixed elements of the composition, wherein the fusible Salt draws the Earth and infusible part into one continuum, and therefore ashes will not run from whence the Salt is drawn, as bone ashes prepared for the Test of Metals. Common fusion in Metals is also made by a violent heat, acting upon the volatile and fixed, the dry and humid parts of those bodies; which notwithstanding are so united, that upon attenuation from heat, the humid parts will not fly away, but draw the fixed ones into fluor with them. Ordinary liquation in wax and oily bodies is made by a