Folktales about luminous gemstones are an almost worldwide motif in mythology and history among Asian, European, African, and American cultures. Some stories about light-emitting gems may have been based on luminescent and phosphorescent minerals such as diamonds.
Mineralogical luminosity
First, it will be useful to introduce some mineralogical terminology for gemstones that can glow when exposed to light, friction, or heat. Note that the following discussion will omit modern techniques such as X-rays and ultraviolet light that are too recent to have influenced folklore about luminous gems. Luminescence is spontaneous emission of light by a substance not resulting from heat, as distinguished from incandescence, which is light emitted by a substance as a result of heating. Luminescence is caused by the absorption of energy that is released in small amounts. When the energy comes from light or other electromagnetic radiation, it is referred to as photoluminescence; which is divisible between fluorescence when the glow ceases immediately with the excitation and phosphorescence when the glow continues beyond the period of excitation. Two types of luminescent phenomena are relevant to crystalline materials. Triboluminescence generates light through the breaking of chemical bonds in a material when it is rubbed, pulled apart, scratched, or crushed. Thermoluminescence re-emits previously absorbed electromagnetic radiation upon being heated (e.g., thermoluminescence dating).
The American geologist Sydney Hobart Ball, who wrote an article on "Luminous Gems, Mythical and Real", outlined the history of discoveries about luminescent and phosphorescent minerals. Most diamonds are triboluminescent if rubbed with a cloth, and a few are photoluminescent after exposure to direct sunlight. Both diamonds and white topaz may phosphoresce if heated below red heat. The phosphorescent quality of diamonds when heated by sunlight is usually believed to have been first revealed by Albertus Magnus (c. 1193–1280) and it was apparently rediscovered by Robert Boyle in 1663, who also found that some diamonds will luminesce under pressure. According to Prafulla Chandra Ray, the Indian king Bhoja (r. 1010–1055) knew that diamonds can phosphoresce.
The luminescent Bologna Stone (impure barite), which was discovered by Vincenzo Cascariolo in 1602, was sometimes called "" ("lunar stone"), because, like the moon, it gave out in the darkness the light it received from the sun. In 1735, the French chemist Charles François de Cisternay du Fay determined that lapis lazuli, emerald, and aquamarine were luminescent. Josiah Wedgwood, in 1792, found phosphoresce from rubbing together two pieces of quartz or of agate, and wrote that the ruby gives "a beautiful red light of short continuance."
Edmond Becquerel reported in 1861 that ruby fluoresces better than sapphire, red feldspar fluoresces, and crushed orthoclase will flame. In 1833, David Brewster discovered the fluorescence of the mineral fluorite or fluorspar. However, the English naturalist Philip Skippon (1641–1691) stated that one Monsieur Lort, of Montpellier, France, a "counterfeiter" of "amethysts, topazes, emeralds, and sapphires" found that on heating "fluor smaragdi" (Latin for "flowing emerald/beryl/jasper") in a pan of coals and afterwards "putting it in a dark place (it) shines very much: At the same time several other stones were tried but did not shine" (1732 6: 718).
Some fluorite, particularly the variety chlorophane (aka pyroemerald and cobra stone), may become very faintly luminescent simply from the heat of one's hand. Chlorophane is unusual for combining the properties of thermoluminescence, triboluminescence, phosphorescence, and fluorescence; it will emit visible spectrum light when rubbed, or exposed to light or heat, and can continue emitting for a long period of time. Among the gravels of the Irtysh River, near Krasnoyarsk, Russia, the German mineralogist Gustav Rose recorded seeing chlorophane pebbles that shone with brilliancy all night long, merely from exposure to the sun's heat. For luminous gem myths, Ball concludes that while it is "not impossible that the inventors of certain of the [luminous gem] tales may have been acquainted with the luminosity of gems, in my opinion many of the tales must be of other origin".
Scholars have proposed many identifications for myths about luminous gemstones described for over two thousand years. Most frequently rubies or carbuncles (often red garnets), which classical and medieval mineralogists did not differentiate, and less commonly other gems, including diamonds, emeralds, jade, and pearls.
The American sinologist Edward H. Schafer proposes that the phosphorescent "emeralds" of classical antiquity, such as the brilliantly shining green eyes of the marble lion on the tomb of King Hermias of Atarneus (d. 341 BCE) on Cyprus, were fluorite, even though the Hellenistic alchemists had methods, "seemingly magical, of making night-shining gems by the application of phosphorescent paints to stones", the most famous being their "emeralds" and "carbuncles".
The names of some luminescent gemstones etymologically derive from "glow" or "fire" words (e.g., pyroemerald for "chlorophane" above). The OED defines pyrope (from Greek Πυρωπός, lit. "fire-eyed")" as: "In early use applied vaguely to a red or fiery gem, as ruby or carbuncle; (mineralogy) the Bohemian garnet or fire-garnet"; and carbuncle or carbuncle-stone (from Latin "carbunculus", "small glowing ember") as: "A name variously applied to precious stones of a red or fiery colour; the carbuncles of the ancients (of which Pliny describes twelve varieties) were probably sapphires, spinels or rubies, and garnets; in the Middle Ages and later, besides being a name for the ruby, the term was esp. applied to a mythical gem said to emit a light in the dark".
Mythological luminosity Luminous gems are common theme in comparative mythology. Ball cross-culturally analyzed stories about luminous stones and pearls and found about one hundred variants in ancient, medieval, and modern sources. The wide-ranging locations of the tales comprise all Asia (except Siberia), all Europe (except Norway and Russia), Borneo, New Guinea, the United States, Canada, certain South American countries and Abyssinia, French Congo, and Angola in Africa. The later African and American myths were likely introduced by Europeans. Ball divides legends about luminous gems into three principal themes: light sources, gem mining, and animals.
Light source legends The first theme is using legendary luminous gems to illuminate buildings, for navigation lights on ships, or sometimes as guiding lights for lost persons.
In India, the earliest country in which fine gemstones were known, belief in luminous gems dates back some twenty-five centuries. The c. 700 BCE – 300 CE Vishnu Purana states that Vishnu, in his avatar as the many-headed snake Shesha under the name Ananta ("Endless"), "has a thousand heads adorned with the mystical Swastika and in each head a jewel to give light". The c. 400 BCE – 300 CE Hindu classic Mahabharata tells the story of the five Pandava brothers and the raja Babruvahana's palace with its precious stones that "shone like lamps so that there was no need for any other light in the assembly." In the c. 100 CE Buddhacarita, the city of Kapila is said to have gems so bright "that darkness like poverty could find no place".
In Classical antiquity, the Greek historian Herodotus (c. 484–425 BCE) was the first European to describe luminous gems. The temple of Heracles at Tyre had two great columns, one of gold, the other of smaragdos (, "green gems including emerald") that "shone brightly at night" (Harvey 1957: 33, suggesting the phosphorescent "false emerald" type of fluorspar). Ball says that the "wily priests doubtless enclosed a lamp in hollow green glass, to mislead the credulous". The Pseudo-Plutarch "On Rivers", probably written by the Greek grammarian Parthenius of Nicaea (d. 14 CE), states that in the Sakarya River the Aster (, "star") gem is found, "which flames in the dark", and thus called Ballen (the "King") in the Phrygian language. The Roman author Pliny the Elder (23–79 CE) described the chrysolampis as an eastern gem, "pale by day but of a fiery luster by night". The Syrian rhetorician Lucian (c. 125–180 CE) describes a statue of the Syrian goddess Atargatis in Hierapolis Bambyce (present-day Manbij) with a gem on her head called Greek lychnis (, "lamp; light"). (Schafer 1963: 237). "From this stone flashes a great light in the night-time, so that the whole temple gleams brightly as by the light of myriads of candles, but in the daytime the brightness grows faint; the gem has the likeness of a bright fire" (tr. Strong and Garstang 1913: 72). According to Pliny, the stone is called lychnis because its luster is heightened by the light of a lamp, when its tints are particularly pleasing.
Although early Chinese classics from the Eastern Zhou dynasty (770–256 BCE) refer to luminous gems (e.g., "the Marquis of Sui's pearl" discussed below under grateful animals), Sima Qian's c. 94 BCE Han dynasty Records of the Grand Historian has two early references to using them as a source of light. Most Chinese names for shining pearls/gems are compounds of zhū (珠, "pearl; gem; bead; orb"), such as yèmíngzhū (夜明珠, "night luminous pearl"), míngyuèzhū (明月珠, "luminous moon pearl"), and yèguāngzhū (夜光珠, "night shining pearl"). The "House of Tian Jingzhong" history records that in 379 BCE, King Wei of Qi boasted to King Hui of Wei, "Even a state as small as mine still has ten pearls one inch in diameter that cast radiance over twelve carriages in front and behind them."
In the biography of the Han court minister Zou Yang (鄒陽, fl. 150 BCE), he figuratively uses the terms mingyue zhi zhu (明月之珠, "luminous moon pearl") and yeguang zhi bi (夜光之壁, "night shining jade-disk") to illustrate how talented people are lost for lack of recommendations, "If I were to throw a luminous moon pearl or a night shining jade-disk on a dark road in front of someone, who would not grasp their sword and look startled?" The German sinologist August Conrady suggested that the Chinese names mingyuezhizhu and yeguangzhu may have an Indian origin, with analogs in the chandra-kânta ("moon-beloved") gem that contains condensed moonlight and the harinmaṇi ("moon-jewel") name for emerald.
Li Shizhen's 1578 Bencao Gangmu pharmacopeia describes leizhu (雷珠, "thunder pearls/beads") that the divine dragon shenlong "held in its mouth and dropped. They light the entire house at night." Chinese dragons are frequently depicted with a flaming pearl or gem under their chin or in their claws. According to the German anthropologist Wolfram Eberhard, the long dragon is a symbol of clouds and rainstorms, and when it plays with a ball or pearl, this signifies the swallowing of the moon by the clouds or thunder in the clouds. The moon frequently appears as a pearl, and thus the dragon with the pearl is equal to the clouds with the moon. The pearl-moon relationship is expressed in the Chinese belief that at full moon pearls are solid balls and at new moon they are hollow (1968: 239, 382).
Rabbinic Judaism includes a number of references to luminous gems. For example, the first century Rabbi, Rav Huna, says he was fleeing from Roman soldiers and hid in a cave illuminated by a light that was brighter in the night and darker in the day.