All these things are worthy of being carefully investigated to ascertain how and by what artifice nature there operates.

But it is not now my intention to treat fully of this matter.

It seems that in general the regularity which occurs in these productions comes from the arrangement of the small invisible equal particles of which they are composed.

And, coming to our Iceland Crystal, I say that if there were a pyramid such as ABCD, composed of small rounded corpuscles, not spherical but flattened spheroids, such as would be made by the rotation of the ellipse GH around its lesser diameter EF (of which the ratio to the greater diameter is very nearly that of 1 to the square root of 8)--I say that then the solid angle of the point D would be equal to the obtuse and equilateral angle of this Crystal.

I say, further, that if these corpuscles were lightly stuck together, on breaking this pyramid it would break along faces parallel to those that make its point: and by this means, as it is easy to see, it would produce prisms similar to those of the same crystal as this other figure represents.