Theophrastus (371 B.C. – 287 B.C.), Greek philosopher, and the title page of his work De Lapidibus (Latin edition, 1578) ("On Stones") – a work in which Theophrastus classifies rocks and gemstones by common properties, and for the first time describes crystal forms and highlights the appearance of flat faces and edges on crystals.

Theophrastus classified rocks and gemstones based on their behavior when heated, further grouping minerals by common properties, such as amber and magnetite, both of which have attracting power. Theophrastus describes various marbles, mentions coal, which he says is used by metalworkers for heating, describes various metal ores, and was aware that pumice stone was of volcanic origin. He also studied precious stones, emeralds, amethysts, onyx, jasper, etc., and described various "sapphires" which were blue with golden veins, probably referring to lapis lazuli. He knew that pearls came from shellfish, that coral came from India, and spoke of fossilized remains of the organic world. He also considered the practical use of various stones, such as minerals needed for the production of glass and plaster, as well as for making various pigments like ochre.

Pliny the Elder dedicated five volumes of his work Naturalis Historia (77 A.D.) to the classification of "earths, metals, stones, and gems." Not only does he describe many minerals unknown to Theophrastus, but he also discusses their applications and properties. He was the first to correctly identify the origin of amber, for example, as the fossilized remains of tree resin, through the observation of insects trapped in some specimens. He laid the foundations of crystallography by discussing crystal forms, particularly the octahedral form of diamonds. He states that rock crystal is valuable because of its transparency and hardness, and that it can be carved into vessels and utensils. His discussion on mining methods is unparalleled in the ancient world and includes, for example, eyewitness reports of gold mining in northern Spain, a depiction that has been fully confirmed by modern research. Pliny also addresses the issue of fraud and the detection of fake gemstones using several tests, including the scratch test, where counterfeit gems can be marked with a steel file, but genuine ones cannot. These may have been glass imitations of jewellery and gemstones. He records that gem cutters use diamond dust to cut and polish other gems, thanks to its great hardness. He speaks of using one hard mineral to scratch another, which today represents the Mohs scale of hardness. "Diamond is at the top of the series because," Pliny says, "it will scratch all other minerals."

Al-Biruni (Persian scholar, astronomer, mathematician, and naturalist, 973–1048) – wrote a book on minerals and gemstones titled Kitab al-jamahir fi ma'rifat al jawahir (The Book of Precious Stones), in which he provides a detailed description of the colours of many minerals and gemstones. He uses colour as a clear method for identifying minerals and gemstones. He extensively discusses the small differences in colour between minerals from different mines or with varying degrees of purity, linking these differences to their potential impact on their financial value. Al-Biruni’s method of using a hydrostatic balance was precise, and he could measure the density of many different substances, including precious metals and gemstones. In addition to developing the hydrostatic balance, Al-Biruni also wrote extensively on the topic of density, including the different types of density and how they are measured. His work on this subject (the beginnings of experimental methods in the Middle Ages) was highly influential and was later used by scientists such as Galileo and Newton in their research.

Albertus Magnus (13th century), De Mineralibus, 1250 – also known as Albert the Great, a German Dominican friar, philosopher, scientist, and bishop, was one of the most versatile thinkers of the Middle Ages. Even more than his most famous pupil, St. Thomas Aquinas, Albert's interests spanned from the natural sciences to theology. He made contributions to logic, psychology, metaphysics, meteorology, mineralogy, and zoology. In his treatise on minerals (De Mineralibus), he reveals a great deal of personal knowledge about mining, ore extraction, and basic metallurgy – the process of extracting metals from ores. He offers observations on different types of minerals and metals, exploring their "powers," noting the properties of each mineral sample, and provides an alphabetical list of many gemstones. It is clear from his text that he himself conducted a series of experiments with different minerals.