Garnet leads the modern Capricorn list, ahead of onyx, black tourmaline, smoky quartz, jet and malachite. Most of that list answers a description Cornelius Agrippa wrote out for Saturn’s stones in 1533, and a description, unlike a list, is something a reader can still pick up and use.
Agrippa’s chapter on Saturnine things, in Book I of the Three Books of Occult Philosophy, names the stones belonging to Saturn: “the Onix, the Ziazaa, the Camonius, the Saphir, the brown Jasper, the Chalcedon, the Loadstone”. Then it adds a clause that does something the seven names cannot. “And all dark, weighty, earthy things.”
Ziazaa and camonius have no agreed modern identification. The clause at the end has had no such trouble, because it describes stones instead of naming them, and a description survives the loss of a vocabulary.
He does this elsewhere too. The Solary chapter picks out stones “which resemble the rayes of the Sun by their golden sparklings”, and the Lunary chapter takes in “all those stones that are White, and Green”. Saturn’s clause is not the only one of its kind. It is the one that happens to line up with a modern shop shelf, and Capricorn is Saturn’s sign in the second-century scheme Ptolemy set out and nobody has withdrawn.
Running the clause
Take the three words separately, because they do not all pick out the same stones. Dark takes onyx, black tourmaline and jet without argument, and smoky quartz in its browner grades. Garnet qualifies in the deep red almandine that fills most shop trays, though not in the paler pyrope. Malachite is a green so saturated it looks dark at arm’s length and looks like nothing of the kind in the hand. A three-word description is always going to have an edge like that.
Weighty is the term with real content, and it is the one modern lists ignore entirely. Specific gravity is the number for it, the count of how many times heavier a mineral is than the same volume of water. Jet is the clearest case at the light end: Whitby Museum describes it as a gemstone of organic origin, formed from wood that fossilised much as coal did, and wood does not become heavy by being buried. A strand of jet beads and a strand of garnet beads of the same size are not the same object in the hand at all.
Earthy is the loosest of the three and probably the most useful, because it rules out the transparent and the spectacular. Nothing on the Capricorn list plays with light. Not one of the six does anything much as it turns under a lamp, and for a sign whose whole reputation is patience that consistency is doing more work than any individual stone on the list.
Now run the clause forward, at material nobody has put on a Capricorn list, and it produces answers.
The loadstone Agrippa names is magnetite. Lodestone is the naturally magnetised form of it, and minerals.net calls it the only mineral that is a natural magnet. Magnetite is black and it is an iron oxide, and its specific gravity runs 4.9 to 5.2, which is about five times the weight of the same volume of water. All three terms, from a mineral sitting on Agrippa’s own Saturn list and on nobody’s Capricorn shelf. Hematite is the neighbouring case, iron oxide again, grey and metallic at Mohs 5 to 6, and equally absent.
Seven names are finished the day somebody writes them down. A description carries on working on material its author never saw.
Chrysoprase, chalcedony, ruby, garnet
The four sign lists give Capricorn four different stones. Agrippa’s own zodiac table gives chrysoprase. A 1604 Spanish treatise by Morales gives chalcedony. Kunz’s list of 1913 gives ruby, and he got there by calendar, since his tally of month stones in the previous chapter gives December ruby and Capricorn opens at the December solstice. Modern practice took January instead, and January is garnet, because Capricorn spends most of itself there.
Two of those come close to each other without meeting. Chalcedony is on Agrippa’s Saturnine list, so a Spanish compiler working seventy years later, agreeing with Agrippa about nothing else, landed on a stone Agrippa had given to Capricorn’s ruling planet. And onyx, the black entry on the modern list, is itself a chalcedony, so Morales in 1604 and a shop shelf in 2026 point at one mineral through two words four centuries apart.
Whether that counts as an agreement depends on whether a name and a mineral are the same kind of thing. The Libra list meets the same question over chrysolite and peridot and comes down against counting it, and the same answer applies here. Four separate compilers over four centuries, none of them citing an earlier one, is not a tradition anybody inherited. It is where the planet has to do the work instead.
The six materials on the modern list
Garnet is a group. Almandine and pyrope are the species behind most of the red material, both at Mohs 7 to 7.5, and neither name reaches a shop label. Jewelers of America gives January garnet without qualification, so the calendar half of this list is the firm half.
Onyx is chalcedony, which is to say quartz, Mohs 7. Smoky quartz is quartz with a colour, and the colour records two things at once. The Museum of Radiation and Radioactivity at Oak Ridge Associated Universities states that the colour of natural smoky quartz is due to exposure to gamma rays from naturally occurring radionuclides such as potassium-40 and members of the uranium and thorium decay series, and adds that for the quartz to turn grey it must contain trace amounts of aluminium. Radiation on its own does nothing. It needs an impurity to work on.
Black tourmaline is schorl, and tourmaline is a supergroup, so the label names a family. Schorl is Mohs 7 with very poor cleavage, which sounds durable and is, in a single crystal. A great deal of handful-sized raw retail material is not a single crystal but a bundle of sub-parallel columns grown side by side, and a piece like that parts along the contacts between columns instead of through them. One on the shelf here leaves black dust and small chips on a hard surface without any impact worth the name. None of that is a comment on the mineral. Every chip it sheds is itself hardness 7.
Malachite is a copper carbonate hydroxide, Mohs 3.5 to 4, with perfect cleavage in one direction. GIA’s ultrasonic exclusion list has malachite on it for heat sensitivity and not for softness, and the two reasons are worth keeping apart.
Jet has no Handbook of Mineralogy page, the Handbook being a reference for minerals. Whitby Museum says the wood came from trees similar to the modern Monkey Puzzle, the genus Araucaria, and puts jet at 3 to 4 on the Mohs scale. It also gives the identification test in a line. Rubbed on a piece of unglazed porcelain, jet leaves a brown streak.
Agrippa’s clause says nothing about how any of these behave in the hand, and no description ever will. What it does instead is keep selecting. Run the three terms over a mineral shelf today and magnetite passes on all of them, which is more than malachite manages, and magnetite is on none of the lists.
Three of the six have species names to be filed under, and the Crystalance Mineral Library tracks them under quartz, tourmaline and malachite. Jet is absent from it for the same reason it has no Handbook page: the Handbook is for minerals, and jet is a tree.
Sources
- Cornelius Agrippa, Three Books of Occult Philosophy, Book I chs. XXIII to XXV, in Peterson’s edition of the 1651 English translation: esotericarchives.com
- Ptolemy, Tetrabiblos I.17, Robbins translation, on Saturn’s houses: penelope.uchicago.edu
- Minerals.net, magnetite and lodestone: minerals.net
- George Frederick Kunz, The Curious Lore of Precious Stones, 1913, chs. IX and X: gutenberg.org
- Jewelers of America, birthstone list: jewelers.org
- Museum of Radiation and Radioactivity, Oak Ridge Associated Universities, on smoky quartz: orau.org
- Whitby Museum, jet FAQ: whitbymuseum.org.uk
- GIA, gems that should not go in an ultrasonic cleaner: 4cs.gia.edu
