CHEMICAL MICROSCOPY 



Table of Crystal Forms 



0-0 Specks; precipitute often aniorphous-lookiiiji with l)irefriiigent specks seen Avith 



crossed nicols. 

 1-1 Needles (fine) 



distortions — hairs 



aggregates — fans, tufts, sheaves, bundles, rosettes, dendrites of needles; burs; 

 wigs, spirals, balls of hairs 

 2-1 Plates essentially regular (triangles, squares, hexagons, octagons, disks) 



unformed or vague — precrystalline disks, smudge rosettes 



distortions — irregular but not definitely elongate plates, flakes 



skeletons— crosses, stars (formation all one crystal) 

 2-2 Elongate or Directional Plates (diamonds, rhomboids, elongate hexagons, etc.) 



skeletons — X's, flat nail shapes, flat combs, etc. 



twins — hourglass shapes, books, etc. 



aggregates — rosettes of plates; stepped or segmented plates; spears (built of dia- 

 monds) 

 2-2 Blades (thin flat forms with length considerably greater than breadth) 



distortions — irregular blades; splinters, ribbons 



skeletons — serrate and feathered blades 



aggregates — fans, sheaves, rosettes, dendrites of blades 

 3-1 Grains (cubes, polyhedra, pyramids, gems, kernels, sharply angular grains) 



unformed or shapeless — globes, globulites, spherulites; nuggets 



aggregates — granular clumps; sphero-rosettes of kernels; chains of grains 

 3-2 Rods, prisms; spindles, thick coarse needles,— (unimmeasurable cross-section) 



distortions — sticks, wires 



aggregates — fans, sheaves, rosettes, clusters, dendrites of rods, etc. 

 3-2 Regular Tablets (regular plates with thickness) 



distortions — tablets irregular but not definitely elongate 



skeletons — regular forms with thickness (e.g., crosses); regularly branching iso- 

 tropic dendritic skeletons 

 3-3 Elongate Tablets and Bars 



with edges — chisels; thick ribbed blades 



skeletons — thick combs, ladders, etc.; dendritic anisotropic skeletons 



aggregates — clusters of bars; irregular multiformed dendrites 



a single crystal, but if different parts brighten 

 and extinguish independently, the whole 

 must be composed of different simpler crys- 

 tals growing from each other or from the 

 same point. 



The above table summarizes the sug- 

 gested classification, including numerous 

 kinds of distortions, skeletons, and aggre- 

 gates. This is not a final answer to the prob- 

 lem, but shows that the many extremely di- 

 verse kinds of crystals can be grouped in a 

 small number of classes, using primarily the 

 two simple concepts of extension and meas- 

 urement. 



Charles C. Fulton 



HISTORY 



The microscope was invented between 

 1590 and 1609, and thus was available dur- 

 ing the very beginning of scientific chem- 

 istry. Scientists of the 1700's used it to look 

 at all sorts of small things, including natural 

 crystals and such things of chemical nature. 

 Some trvie chemists, as soon as there were 

 any who deserved this name, used it, in an 

 observational way, in their chemical re- 

 searches. 



True "chemical microscopy", although 

 not then known by this name, began at least 

 as early as 1742. In that year "The Micro- 

 scope Made Easy", by Henry Baker, Fellow 



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