Pliny the Elder [1st century CE] (Natural History, Book 9, 54-58): [Book 9, 54] The first place therefore and the topmost rank among all things of price is held by pearls. These are sent chiefly by the Indian Ocean, among the huge and curious animals that we have described as coming across all those seas over that wide expanse of lands from those burning heats of the sun. And to procure them for the Indians as well, men go to the islands — and those quite few in number: the most productive is Ceylon, and also Stoidis, as we said in our circuit of the world, and also the Indian promontory of Perimula; but those round Arabia on the Persian Gulf of the Red Sea are specially praised. The source and breeding-ground of pearls are not much differing from oyster-shells. These, we are told when stimulated by the generative season of the year gape open as it were and are filled with dewy pregnancy, and subsequently when heavy are delivered, and the offspring of the shells are pearls that correspond to the quantity of the dew received: if it was a pure inflow, their brilliance is conspicuous but if it was turbid, the product also becomes dirty in color. Also if the sky is lowering (they say) the pearl is pale in color: for it is certain that it was conceived from the sky, and that pearls have more connection with the sky than with the sea, and derive from it a cloudy hue, or a clear one corresponding with a brilliant morning. If they are well fed in due season, the offspring also grows in size. If there is lightning, the shells shut up, and diminish in size in proportion to their abstinence from food; but if it also thunders they are frightened and shut up suddenly, producing what are called 'wind-pearls', which are only inflated with an empty, unsubstantial show: these are the pearls' miscarriages. Indeed a healthy offspring is formed with a skin of many thicknesses, so that it may not improperly be considered as a hardening of the body; and consequently experts subject them to a cleansing process. I am surprised that though pearls rejoice so much in the actual sky, they redden and lose their whiteness in the sun, like the human body; consequently sea-pearls preserve a special brilliance, being too deeply immersed for the rays to penetrate; nevertheless even they get yellow from age and doze off with wrinkles, and the vigor that is sought after is only found in youth. Also in old age they get thick and stick to the shells, and cannot be torn out of these except by using a file. Pearls with only one surface, and round on that side but flat at the back, are consequently termed tambourine pearls; we have seen them clustering together in shells that owing to this enrichment were used for carrying round perfumes. For the rest, a large pearl is soft when in the water but gets hard as soon as it is taken out. [Book 9, 55] When a shell sees a hand it shuts itself up and conceals its treasures, as it knows that it is sought for on their account; and if the hand is inserted first it cuts it off with its sharp edge, the most just penalty possible - for it is armed with other penalties also, as for the most part it is found among rocks, while even in deep water it has sea-dogs in attendance - yet nevertheless these do not protect it against women's ears! Some accounts say that clusters of shells like bees have one of their number, a specially large and old shell, as their leader, one marvelously skillful in taking precautions; and that these leader-shells are diligently sought for by pearl-divers, as when they are caught all the rest stray about and easily get shut up in the nets, subsequently a quantity of salt being poured over them in earthenware jars; this eats away all the flesh, and a sort of kernels in their bodies, which are pearls, fall to the bottom. [Boo 9, 56] There is no doubt that pearls are worn away by use, and that lack of care makes them change their color. Their whole value lies in their brilliance, size, roundness, smoothness and weight, qualities of such rarity that no two pearls are found that are exactly alike: this is doubtless the reason why Roman luxury has given them the name of 'unique gems', the word unio not existing in Greece, and indeed among foreign races, who discovered this fact, the only name for them is margarita. There is also a great variety in their actual brilliance; it is brighter with those found in the Red Sea, whereas those found in the Indian Ocean resembles flakes of mica, though they excel others in size. The highest praise given to their color is for them to be called alum-colored. The longer ones also have a charm of their own. Those that end in a wider circle, tapering lengthwise in the shape of perfume-caskets, are termed 'probes'. Women glory in hanging these on their fingers and using two or three for a single earring, and foreign names for this luxury occur, names invented by abandoned extravagance, inasmuch as when they have done this they call them 'castanets', as if they enjoyed even the sound and the mere rattling together of the pearls; and now-adays even poor people covet them — it is a common saying that a pearl is as good as a lackey for a lady when she walks abroad! And they even use them on their feet, and fix them not only to the laces of their sandals but all over their slippers. In fact, by this time they are not content with wearing pearls unless they tread on them, and actually walk on these unique gems! [Book 9, 57] It is clear that they are of a firm substance, because no fall can break them. Also they are not always found in the middle of the flesh, but in a variety of places, and before now we have seen them even at the extreme edges, as though in the act of passing out of the shell ; and in some cases we have seen four or five pearls in one shell. In weight few specimens have hitherto exceeded half an ounce by more than one scruple. [Book 9, 58] There have been two pearls that were the largest in the whole of history; both were owned by Cleopatra, the last of the Queens of Egypt - they had come down to her through the hands of the Kings of the East. When Antony was gorging daily at recherche banquets, she with a pride at once lofty and insolent, queenly wanton as she was, poured contempt on all his pomp and splendor, and when he asked what additional magnificence could be contrived, replied that she would spend 10,000,000 sesterces on a single banquet. Antony was eager to learn how it could be done, although he thought it was impossible. Consequently bets were made, and on the next day, when the matter was to be decided, she set before Antony a banquet that was indeed splendid, so that the day might not be wasted,** but of the kind served every day - Antony laughing and expostulating at its niggardliness. But she vowed it was a mere additional douceur, and that the banquet would round off the account and her own dinner alone would cost 10,000,000 sesterces, and she ordered the second course to be served. In accordance with previous instructions the servants placed in front of her only a single vessel containing vinegar, the strong rough quality of which can melt pearls. She was at the moment wearing in her ears that remarkable and truly unique work of nature. Antony was full of curiosity to see what in the world she was going to do. She took one earring off and dropped the pearl in the vinegar, and when it was melted swallowed it. Lucius Plancus, who was umpiring the wager, placed his hand on the other pearl when she was preparing to destroy it also in a similar way, and declared that Antony had lost the battle - an ominous remark that came true. - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 15, 8): The aforesaid stone is produced from a shell resembling a large trumpet-shell, and the Pearl-oysters swim in shoals and have leaders, just as bees, in their hives have kings, as they are called. And I have heard that the leader too is conspicuous for his color and his size. Now divers beneath the waters make it their special aim to capture him, for once he is caught they catch the entire shoal, since it is, so to say, left destitute and without a leader; for it remains motionless and ceases to advance, like a flock of sheep that by some mischance has lost its shepherd. - [Scholfield translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 53.23-27): [Chapter 53.23] This type of stone is found in mollusks. At a fixed time of year, these mollusks run riot because of conception. They thirst after dew as after their mates. For desire of it they gape. When the shower of the moon melts away the most, they drink in the desired moisture with a certain gaping. Thus they conceive and become pregnant. [Chapter 53.24] The condition of the pearls depends on the quality of what the mollusks drink in. For if they accept something pure, the little orbs are white; if it is something murky, they either are tired and pale, or stained with red. [Chapter 53.25] Thus, the mollusks’ offspring are more from the sky than from the sea. As often as the mollusks receive the mist of the morning air, the brighter the pearls become; as often as they receive the evening mist, the darker the pearls become. The more the mollusks drink, the more the stones grow. If a gleam flashes unexpectedly, the mollusks squeeze shut in untimely dread. Blocked up from sudden terror, they draw in abortive defects. The stones either become very small, or nonexistent. [Chapter 53.26] The mollusks have senses. They fear that their offspring will become tainted, and when the day burns with more fiery rays, they sink down into the deep, lest their stones become stained by the rage of the sun. Subsiding into the depths, they protect themselves from the heat. Age brings relief to this providence. For radiance is destroyed by it, and the pearls in the growing mollusks turn yellow. The pearl is soft in water, and hardens when removed. [Chapter 53.27] Two the same are never found: thence the name uniones was given. They deny they are found above a semuncia in size. Mollusks fear the ambushes of fishermen. Thence it is that most of them hide either between the rocks or amongst the sea-dogs. The mollusks swim in flocks. A swarm has a designated leader; if he is captured, then even those who escaped turn back into the nets. - [Arwen Apps translation, 2011]

Saint Ambrose [4th century CE] (Hexameron, Book 5, 11.33): We see how nature has inserted in the oyster a highly valuable pearl, which by the action of sea water has become a solid particle within the oyster's soft flesh. - [Savage translation, 1961]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6, 49; 6, 51-53): [Book 12, 6:49] There are many kinds of shellfish, among which some are pearl-bearing. These are called oceloe; the precious stone is solidified in their flesh. People who have written on the nature of animals say concerning these creatures that they seek the shore at night, and conceive the pearls by means of celestial [caelestis] dew; hence they are called oceloe. [Book 12, 6:51] [Crabs] are animals hostile to oysters. With marvelous ingenuity they live on oyster flesh, for, because the oyster’s strong shell cannot be opened, the crab spies out when the oyster opens the closed barricade of its shell, and then stealthily puts a pebble inside, and with the closing thus impeded, eats the oyster’s flesh [Book 12, 6:52] The oyster [ostrea] is named from the shell with which the inner softness of its flesh is guarded... [Book 12, 6:53] The mussel is a shellfish from whose milt oysters conceive... - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.53; 7.61): [Fish 7.53] Pearls, as Solinus says, are made in this way: the shells in which they are found cling to the shore at night, and by the dew of the sky they conceive pearls; if what they have received was pure, they are white gems; if impure, they either languish with pallor or are clouded and rough. Finally, every time they receive the seed of the morning air, the pearl becomes brighter; every evening, it becomes darker; and the more dew it receives, the greater the size of the stone becomes. If lightning suddenly flashes, they are crushed and closed by sudden fear, so they either miscarry or produce smaller gems. Such shells themselves have senses, so that they fear their births will be stained. When the sun has sent forth burning and boiling orbs, lest the stones should be darkened by excessive heat, the shell sinks into the depths. Two are never found in one shell: whence they are called uniones by most. As sun shines down, the stones turn yellow. They are afraid of the traps of fishermen, and therefore they often hide among the rocks. They swim in flocks, and the one who is more experienced among them leads the flock; if it is captured the others return and are also caught. A pearl is soft in water, but when taken out it hardens into stone. They are not found beyond half an ounce. And they say that when they are living in the shell they grow and shrink as the Moon waxes and wanes. There are a great differences in their brightness. It is the highest praise of the color, when the glowing gems are colored like like alum. There are some which are appear in an oblong shell and thus are longer. To hang two or three of these pearl gems on the fingers or ears is the glory of women. They dissolve quickly when placed in vinegar. Whence we quote it from Pliny: There were two very great pearls that Cleopatra, the last of the queens of Egypt, had, given to her by the kings of the East. Therefore, when Antony, her husband, was feasting every day on exquisite feasts, the harlot queen began to insult his feasts with a impertinent countenance, claiming that she would spend six and sixty times as much at one meal, that is, a hundred times as much as he would spend at feasts. At this the king was astonished. After the wagers had been made, Cleopatra sat down at the table, and having brought before her only a vase of vinegar, she drew from her ears a single pearl. When she had thrown it in vinegar, it dissolved and the queen drank the liquid. When she prepared to dissolve the other one, the judge, not wanting to destroy that singular work of nature for a royal bet, soon pronounced Antony defeated. It has, as they say, both strength and harmony, and it confers health of mind and body, indeed of the mind because it renders the wearer chaste. [Fish 7.61] Oysters, as Pliny says, are a species of shells or snails, on the flesh of which the crabs live by their wonderful ingenuity. For when they are not able to open their shells, they wait in ambushes, and when the oyster opens its shell, the crabs throw stones inside, and thus hinder their closing by blocking them with stones, and gnaw their flesh. [Thomas repeats this story in his description of the crab (7.19) ]- [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.26): Oysters bee called Oilica, and have that name of shelles, that defend and warde softe fish within. And the Greekes call an Oyster T•ll•m, and all that Fish with the shells is called Ostrium in the Newter gender: but the Fish thereof and the meate that is wtin the shels, is called Ostrea in the Feminine gender: And such shell Fish bee called Conche and Conchilia also: for when the Moone falleth, such Fishes bee voide: And the waxing of the Moone increaseth the humoure, and the humoure vanisheth, when the Moone vanisheth. And therefore shell Fish ware, when the Moone wareth, and bée voyde, when the Moone waneth. And in shell Fish bée Pearles bread. And thereof speaketh Plinius and other that write of such things. For by night shell Fish come to cliffes, and conceive Pearles of the dewe of Heaven. And therefore the shell Fish be called Conchile and Margarete, and Herelie, when in theyr fish precious stones be pight. And that precious stone that is gendered of dewe in Springing time, is most worthy and noble, and the more white and bright he is, the more effectuall and vertuous it is held. - [Batman]