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Theophrastus from Efeso (ca. 372 -ca. 287 b.c.) is certainly the most important scientist of the classic period even if not the most influent. He dedicated much time to gather information on scientific knowledge from other authors in order to organize , summarize and rewrite them in his own manner and to transmit to students. He also produced a number of original works following the path of Aristotele , his master, of whom he was the follower.
He was so important for the culture of the time that Plinius in his Historia Naturalis mentions him, second only after Varrone, the most important Roman scientist, as the major source for his gigantic opera. During old times (middle III cent. BC) there were 224 works of Teophrastus mentioned by Diogene Laerzio, but most of them disappeared, probably because his science was directly used by Plinius. Only 11 reached us through direct tradition (copy of the original in Greek or Latin); of some others there are only isolated fragments from which it is very difficult to put together a reasonable reconstruction of the work.
His most famous works are ‘ De plantarum’ (on flowers), ‘De Odoribus’ and ‘Characters’.
He wrote a work on stones ‘De Lapidibus’ and probably one on metals and metallurgy ‘De Metallis’.

It is a work of special interest in the history of mineralogy as it is the largest fragment to survive from Classical times that treats mineral substances in a systematic way. It is like no other mineralogical work written during the period, and in fact no other original work resembling it appeared until the Middle Ages. It remained for 1800 years one of the most authoritative treatise on minerals,referenced and quoted by writers down to modern times.
The comparative absence from myth and magic in the descriptions is particularly noteworthy, and shows there existed, probably among miners, quarryman, and others engaged in the mining industry of the time, a practical knowledge of mineralogy, which Theophrastus drew upon in the compilation of this work. The text, written as a series of 69 paragraphs, suggests the Peri Lithon to be a series of lecture notes rather than a formal treatise (Adams, 1934). Some passages contain obvious additions that appear to be notes appended to the more detailed information. It seems possible, therefore, that Peri Lithon is a set of lecture notes as the author would have delivered in the gardens of the Lyceum almost two millennia ago. Incredibly, the text of the treatise appears to have come
down to the present little changed from what it was in the beginning. All surviving ancient works, have made their way through time by a tradition of manuscript copying. Invariably, as scribes copied manuscripts, mistakes were unwittingly introduced. The fact that this work exists in a relatively few manuscripts that when compared show few differences, suggests that Peri Lithon is probably very close to what Theophrastus originally wrote.
Metals are said to be composed of water, while stones and mineral earths are composed of earth. A mineral occurs because its substance has been purified through filtration, and its degree of purity can be determined by examining such qualities as smoothness, density, luster and transparency. The primary interest in the work are the descriptions of specific minerals.
Theophrastus divides into two broad categories, Earths and Stones, under which about fifty “species” are recognized. Within each commentary, the author recounts various physical characteristics such as texture, color, transparency, hardness, luster, and density, as well as the practical uses. Thus described, it is possible to apply modern names to many of the minerals Theophrastus wrote about eighteen centuries ago, and read the Classical ideas about marble,
pumice, onyx, gypsum, amber, pyrite, coal, azurite, chrysocolla, realgar, orpiment, cinnabar, quartz, lapislazuli, emerald, sapphire, ruby and diamond. By recording the properties of the species, this
early work set a high standard over other mineralogical writings of the period. Theophrastus is in fact the first investigator to methodically treat mineral substances for themselves rather than for their magical or curative properties, and he may be considered the best and most accurate mineralogist among the ancients.