Nearly all of the stones mentioned by Posidippus are also treated by Theophrastus, the exceptions being the snakestone (AB 15), the conjectural reading of Beryllion (AB 6.3), and of course the great boulder used at the end to praise the power of Poseidon (AB 19).

From parallels such as this it is clear that Posidippus is relying to some degree on technical writing. One or two instances of such technical correctness could be explained by personal experience or hearsay, but for the whole we need to posit the presence of technical sources from which Posidippus could mine his details about stones and their exceptional properties.

In order to clarify the relationship between Posidippus and technical writings such as we possess by Theophrastus and Pliny, I will examine four of the epigrams in the Lithika section, noting the intersections between the epigrams and technical writing. The goal of the readings will be not only to find these references, but further to note how this technical information allows us to update or deepen our interpretation of the epigram. We begin with the first epigram in the collection that is reasonably complete (AB 5):

Theophrastus gives a slightly different spelling for this stone (which we know as lapis lazuli), but any doubt as to whether he refers to the same stone is allayed by the brief description: ‘[it] is speckled with gold’ (αὕτη δ᾿ ἐστιν ὥσπερ χρυσόσπαστος) (IV 23). In a later mention of the stone Theophrastus adds that the stone is ‘dark’ (μέλαινα (VI 37). It is also (IV 23) classed among ‘stones, of which signets are carved’ (ἐξ ὧν καὶ τὰ σφραγίδια γλύφουσιν).

In highlighting the process of exchange, this short epigram becomes a useful entrance to the poetic project of Posidippus. In the Lithika, but also notably in the Oiônoskopika section, Posidippus is taking over knowledge whose natural domain might be thought to rest in didactic poetry or scientific treatises. But the manifest lack of scientific system, and the presence of the long epigram on a great boulder (AB 19), betray the fact that Posidippus did not intend to write a poetic textbook on gems in a way parallel to Aratus’ poetic translation of a textbook on constellations and weather signs. Rather, in the same way that the stone is worked by a craftsman and transformed into an object exchanged for a kiss, the technical writing of a scientific philosopher such as Theophrastus is skillfully re-worked until it becomes a work that gives aesthetic pleasure.

Posidippus goes further than mere correctness in this epigram, he may also be interested in critiquing an earlier opinion on the stone xanthe. In a short note Theophrastus takes issue with the color of xanthe, writing that it is ‘not so much yellow in color as whitish’ [or ‘off white’] (οὐ ξανθὴ μὲν τὴν χρόαν, ἔκλευκος μᾶλλον) (VI 37). He buttresses this with an explanation that the word xanthos means ‘whitish’ for speakers of Doric Greek, not yellow.

When we turn back to the epigram we notice that color gets emphasized to an unusual degree. Both the third and sixth lines describe the stone as ‘honey-colored’, as if he could not quite trust the word xantha to stand by itself for the color. Then perhaps to prove his point, he sets the stone on the truly white skin of Niconoe’s breast. Given this beautifully white background, the yellowness of the stone stands out vividly in the reader’s imagination, and the doubts of the scholar who might remember the description of Theophrastus are banished.

Although the number of conjectures in this epigram is quite large, it is clear that Posidippus is contrasting two states, first oiled or wet, then dry, and two different ways that light responds to this stone.

I would like to suggest that the stone smaragdos, a name for a class of green precious stones, is a possible solution to this riddle epigram. Theophrastus twice singles out a remarkable power: its ability to lend its color to a body of water that surrounds it.

When Pliny writes about the stone he also lingers over the unique optical power of the smaragdos, though applying the effect to the air rather than to water:

The mechanism may be suspect, but his meaning is quite clear: the air that bounces up against the stone is colored, and thus when viewed from a distance the stone naturally looks larger.

Oddly, the eyes of cats, real or statue, figure in both of these examples from Pliny, and it is interesting that in the editorial restoration of line 31 we find a lion.

It thus seems plausible to understand this short epigram as a reference to the stone smaragdos. The optical quality of light literally ‘running around’ (περιθεῖ) the mass, as described by Posidippus, seems closely connected to the optical effect of the stone in both Theophrastus and Pliny. And the second quality of blazing solves nicely the last two lines of the epigram. And these dual optical effects seem sufficient to earn for a stone the title ‘crafty’ (κερδαλέη).

Unlike the other stones mentioned above, the snakestone does not correspond to an actual stone. Pliny starts off with a general account of the supposed origin of this stone:

We should imagine a stone smaller than the head of a snake, streaked with white, and with one streak containing an engraved chariot which is impossible to see with the naked eye but which shows up clearly when an imprint is taken.

The internal references to the eyesight of a stoneworker are compatible with this reading. There are two references to the eyesight necessary for this kind of carving: line 4 with the reference to the incredible vision of the Argonaut Lynceus, and lines 6–7 with the note that it is a ‘wonder’ (θαῦμα) that the stoneworker did not damage his eyes by such minute attention. The reader encounters the stone through the eyes of the narrator, and follows the narrator’s reasoning about the necessity of superhuman eyesight and miraculous craft in order to make such a carving. But the reader may well begin to wonder about the conclusions drawn by the narrator, since the conclusions seem to point to a level of skill that is impossible for a human being. One begins to question the reliability of the narrator since this stoneworker is too skilled, the vision required is too great, for an actual stoneworker to have carved the invisible chariot upon the streak of white. Then if the reader recalls the note by Sotacus that this is a stone which cannot be carved, the true nature of this stone appears: it is a natural wonder, a self-carved stone. The hidden riddle mirrors the hidden carving present on the snakestone.

It is also possible to read this in a different way. One could argue that this is another case of Posidippus subtly correcting his source, either by the use of information gained from some other technical source, or by personal knowledge of some stone that was purported to be a snakestone. Posidippus, on this reading, affirms the basic facts about the origin and color of the snakestone as presented by Sotacus, but then differs by presenting a case where the snakestone has been successfully carved. As with the Xanthe discussed earlier, the point is to be aware of Posidippus’ subtle correcting of his sources.

The snakestone contains a design invisible to the eye glancing upon it, a design that appears only after an imprint is taken. It is a picture of the process that a reader must go through in understanding these epigrams: there is a brilliance invisible at first, but which becomes visible as soon as one is willing to delve into its more elusive aspects.