Moonstone. Pearl, ruby, carnelian, rose quartz and selenite make up the rest, and two of those six were already the Moon’s stones in 1533. Neither of the two is moonstone.
In 1533 Cornelius Agrippa wrote out the things belonging to the Moon, and among the stones he named one that behaves like her. “The stone Selenites,” he calls it, “shining from a white body, with a yellow brightness, imitating the motion of the Moon, having in it the figure of the Moon which daily increaseth, or decreaseth as doth the Moon.”
He is describing something chosen for what it does. Composition was not available to him and he claims no pedigree for it anywhere. The stone is on his list because something in it waxes and wanes.
A line later he names pearls among the Moon’s things too, along with crystal, silver marcasite, beryl, and all stones that are white and green. Pearl is on the modern Cancer list. A stone called selenite is on it as well. Agrippa’s own table of sign stones, printed in his second book, gives Cancer chalcedony and none of this.
What Agrippa gave the Moon
Set the Lunary chapter beside a shop shelf and the two describe each other better than either describes the sign lists in between. Agrippa’s Moon stones are not named by species, which was not available to him, and not by origin. They are named by how they look and what they do: white, green, shining from a white body with a yellow brightness, carrying a figure that changes. That is a description of behaviour, and almost every stone on the modern Cancer list is pale and either translucent or softly reflective. Pearl, moonstone, rose quartz and selenite would all pass it without argument.
What stone he meant by Selenites is a separate question, and not a settled one. The name is old and it has been attached to more than one material over the centuries. What now carries it is a variety of gypsum, and gypsum does not do the thing Agrippa describes. It holds no changing figure and throws no moving light. Moonstone does. Whether he was looking at gypsum or at a feldspar, the description he left is a description of adularescence, the soft light that seems to float below the surface of a stone and slide across it as the piece is tilted.
The continuity here is real and it is narrower than it first looks. What survived four centuries is not a stone name matched to a sign. It is an account of why a moon-like appearance belongs to the Moon, and modern practice arrived at the same account without needing to read him.
The argument underneath the rulership
The rulership is older still and, unusually for this subject, it comes with reasoning attached. Ptolemy set out the planetary houses in the second century. Cancer and Leo, he writes, are “the most northern, which are closer than the others to our zenith and therefore most productive of heat and of warmth”, so they were assigned to “the greatest and most powerful heavenly bodies, that is, to the luminaries, as houses, Leo, which is masculine, to the sun and Cancer, feminine, to the moon”. The five remaining planets take two signs each, one from the solar half of the circle and one from the lunar, ordered by distance from those two lights.
Cancer and Leo are therefore the only two signs in the scheme that do not share a ruler, and that asymmetry sits in the second-century text and was not added later for colour. The reason Cancer went to the Moon is also an argument about which signs stand highest and hottest in the sky. Water does not come into it, and neither do tides.
Marsilio Ficino, in 1489, gives a shorter list than Agrippa’s and a different answer. Carbuncle and pantaura chiefly to the Sun, sapphire to Jupiter, emerald to Venus, to Mercury and to the Moon. On that authority the Moon holds a green beryl jointly with two other planets, and holds nothing on its own. Two Renaissance writers, forty-four years apart, and no overlap between their answers for the same body.
Four compilers and no overlap
The sign lists, as against the planet chapters, hand Cancer four different stones. Agrippa’s 1533 table gives chalcedony, on a row that carries the twelve months as well as the twelve signs. Morales, whose 1604 Spanish treatise reaches us only because Kunz reprinted it, gives agate and beryl. Kunz himself gives emerald, reached through his tally of month stones in the previous chapter, where June ties between emerald and agate. A shop today hands over moonstone.
Chalcedony, agate and beryl, emerald. Not one of the three older answers is moonstone, and no two of the four compilers were reading each other. That is why nobody can appeal to a tradition here. There is no single ancestor list for the twelve signs to appeal to.
The calendar is where the rest of the modern list came from. Cancer runs from about 21 June to about 22 July, so it inherits both months from the birthstone list Jewelers of America maintains, and June carries pearl, moonstone and alexandrite while July carries ruby. Alexandrite is the one calendar stone that never turns up on a Cancer shelf, since a colour-change chrysoberyl is a jeweller’s gem at a jeweller’s price and the crystal trade deals in material people can pick up for a few pounds.
The six materials
Pearl is not a mineral. What a mollusc lays down is nacre: aragonite, a form of calcium carbonate, in fine layers bound with a protein called conchiolin. There is no Handbook of Mineralogy page for it and no place on the International Mineralogical Association’s list of valid species, because a biological product is excluded by the definition. That has never kept it off a June ring and there is no reason it should.
Moonstone is not a species either. It is an adularescent alkali feldspar, and the Handbook’s entry for orthoclase records only that the mineral may exhibit opalescence or schiller iridescence, which is as close as a reference work comes to the effect the whole trade is named for.
Ruby is the red variety of corundum, aluminium oxide, Mohs 9, brittle but tough when compact and with no true cleavage. Carnelian is chalcedony, so quartz, Mohs 7. As for rose quartz, GIA states that it is generally stable when exposed to light and heat, which is not true of everything the trade files alongside it.
Selenite is the one where carelessness costs something. The Handbook puts gypsum at Mohs 1.5 to 2 with perfect cleavage in one direction and describes it as flexible and inelastic. A fingernail marks it. The National Park Service, explaining how the dune field at White Sands forms, states that gypsum “is an evaporate mineral–it dissolves in water and will recrystallize during evaporation of liquid, much like salt”. That page is about dunes and not about shelves, but a mineral that dissolves in a desert dissolves in a bowl on a windowsill.
Two of the six have no page of their own in the Crystalance Mineral Library. Moonstone is filed under feldspar, selenite under gypsum, and pearl is not there at all.
Somebody in 1533 wrote down a stone that carries a figure of the Moon in it, and the figure grows and shrinks as the Moon does. Four hundred years later a shop puts a moonstone cabochon in a tray for the same sign, and nobody in between passed the sentence along.
Sources
- Cornelius Agrippa, Three Books of Occult Philosophy, Book I ch. XXIV on Lunary things and Book II ch. XIV, in the 1651 English translation of the 1533 original: esotericarchives.com
- Ptolemy, Tetrabiblos I.17, Robbins translation: penelope.uchicago.edu
- Marsilio Ficino, De vita libri tres, Book III, Lyon 1560: archive.org
- George Frederick Kunz, The Curious Lore of Precious Stones, 1913, chs. IX and X: gutenberg.org
- Jewelers of America, birthstone list by month: jewelers.org
- GIA, rose quartz care and cleaning: gia.edu
- National Park Service, White Sands, on gypsum: nps.gov
