Garnet
Garnet is the most misunderstood stone in the case, because almost everyone thinks it is one thing. It is a family.
Is garnet one stone or many?
Garnet is a group of related silicate minerals that share a crystal structure and differ in chemistry. That chemistry decides the colour. Almandine runs deep red to brownish-red. Pyrope is the bright, clean red. Rhodolite sits between the two and reads raspberry to violet. Spessartine is orange, tsavorite is green, demantoid is a green that outshines most emerald.
So "garnet" tells you about as much as "quartz" does. The variety name is the useful information.
Is garnet treated?
Garnet is one of the very few gemstones that is essentially never treated. No heat, no irradiation, no oiling, no dye. The colour you are looking at is the colour it grew with. In a market where treatment is the norm, that is worth something — and it means a garnet's price reflects the stone, not what was done to it afterwards.
What should you look for in garnet?
Colour first. The common failure in red garnet is going too dark: past a certain saturation the stone reads black in anything but direct light, and no amount of cutting rescues it. Hold a candidate under ordinary indoor light rather than a jeweller's lamp — that is where it will live.
Garnet has high refractive index and disperses light well, so a well-cut stone has real life in it. Poorly cut, it goes flat and glassy. Depth of cut matters more here than in most stones.
Is garnet durable enough for daily wear?
Mohs 6.5 to 7.5 depending on variety — harder than turquoise or opal, softer than sapphire. Perfectly sound for a ring worn daily, provided it is set with some protection at the girdle. Garnet is brittle at the edges and will chip if knocked against a doorframe often enough.
How do you care for garnet?
Warm water, mild soap, soft brush. Garnet takes cleaning better than almost anything else we set. Avoid steam and sudden temperature change — thermal shock is the one thing that reliably damages it.
Why is garnet January's birthstone?
Garnet is January's birthstone, which is why it moves in December. Historically it travelled with people rather than staying in vaults: carried as protection on journeys, set into rings meant to be worn rather than displayed. Fitting, for a stone that survives daily wear better than its reputation suggests.