gems, gemology, history of gemology, gem testing, mineralogy, early mineralogy, jasper, topaz, amber, gem formation

Sinkankas: Henkel presents his views on the formation of minerals, including coral and gemstones, with extensive annotations by Zimmermann. He recognized five modes of formation: (1) congelation, (2) concretion, (3) vegetation (as in coral), (4) crystallization, and (5) petrifaction. Henkel believed that durable minerals—especially gemstones—were composed of minute particles that grew together into structurally continuous masses or crystals, producing transparency while excluding water. He discusses at length, as does Zimmermann, experiments by Robert Boyle, Francis I, and others on the effects of intense heat on gemstones, describing the behavior of diamond, emerald, ruby, and other gems. Additional topics include Saxon fossil resin (pp. 539–553), the celebrated Saxon topaz (pp. 554–565), and a green jasper bearing “hieroglyphic figures” (pp. 607–619), possibly referring to graphic granite. The work is described by John Ferguson in Bibliotheca Chemica (Vol. I, p. 386), which also notes later editions published in 1747 and in Vienna in 1769, together with biographical and bibliographical information on Henkel and his writings.