What two categories of carbon did Rosalind Franklin distinguish in her coal research?

Rosalind Franklin distinguished graphitizing and non-graphitizing carbon in her coal research.

She developed this classification while studying what happens to carbon-rich materials during heating. Graphitizing carbons can reorganize into crystalline graphite when heated to sufficiently high temperatures. Non-graphitizing carbons resist that transformation and retain a more disordered, cross-linked structure even at extreme temperatures.

The distinction reflected differences in how carbon atoms are arranged during carbonization. Graphitizing materials generally pass through a fluid or mobile stage, allowing aromatic structures to align and form graphite-like layers. Non-graphitizing materials do not normally pass through that stage; cross-links between smaller structural units restrict their movement and prevent graphitization.

This terminology is easy to confuse with physical descriptions such as hard, soft, porous, or non-porous. Those properties often differ between the two categories, but they are not the names of Franklin's classification. Her coal and carbon studies were conducted before and during her later DNA work, and they helped establish her reputation as an expert X-ray crystallographer.