Plum Tourmaline Identification Guide
How to identify plum tourmaline by its purple-red elbaite color, striated prisms, strong pleochroism, and hardness, and how to tell it from amethyst, garnet, and ruby.
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What Plum Tourmaline Looks Like
Plum tourmaline is a purplish-red to reddish-purple variety of elbaite tourmaline, sitting between rubellite (pink-red) and purple tourmaline. Its color resembles a ripe plum — deep, slightly muted purple-red. Luster is vitreous, and quality stones are transparent to translucent. The hallmark habit is long prismatic crystals with a rounded triangular cross-section and strong lengthwise striations running parallel to the crystal's long axis.
Step-by-Step Field ID Checklist
- Examine the crystal cross-section. A rounded triangular (trigonal) outline is classic tourmaline and rules out most look-alikes.
- Look for striations. Strong parallel grooves along the length of the prism are diagnostic.
- Check pleochroism. Rotate the stone in light — plum tourmaline shows two distinctly different shades (strong dichroism), often darker down the length of the crystal.
- Note color zoning. Tourmaline frequently shows color changes along or across the crystal.
- Test hardness. It scratches glass and quartz readily.
Key Diagnostic Tests
- Mohs hardness: 7 to 7.5 — scratches quartz.
- Cleavage: Essentially none (very poor); uneven to conchoidal fracture.
- Streak: White.
- Specific gravity: About 3.0 to 3.1.
- Pleochroism: Strong — a key separator from garnet and amethyst.
- Crystal form: Trigonal prisms, rounded triangular section, striated.
Common Look-Alikes and How to Tell Them Apart
- Amethyst / purple quartz: Softer (7), hexagonal habit, weak pleochroism, no triangular cross-section.
- Almandine / rhodolite garnet: Isometric (no prisms, no striations), singly refractive (no pleochroism), and denser.
- Ruby / pink sapphire: Much harder (9), barrel-shaped hexagonal crystals, higher density.
- Purple/plum spinel: Octahedral crystals, isometric, no pleochroism.
- Kunzite (spodumene): Shows perfect cleavage (tourmaline does not) and strong pleochroism but a different lilac-pink tone.
Where Plum Tourmaline Is Found
Gem elbaite in plum hues comes from the great tourmaline pegmatite districts: Minas Gerais (Brazil), Madagascar, Nigeria, Afghanistan and Pakistan, and California and Maine (USA). It occurs in granitic pegmatites alongside quartz, lepidolite, and other colored tourmalines.
Frequently asked questions
How can you tell if it's real plum tourmaline?
Look for a rounded triangular crystal cross-section, strong lengthwise striations, strong pleochroism (two color shades when rotated), hardness of 7 to 7.5, and no cleavage. These together confirm tourmaline over amethyst or garnet.
What does plum tourmaline look like?
It is a deep purplish-red to reddish-purple gem, glassy and transparent to translucent, typically as striated prismatic crystals with a triangular cross-section.
Plum tourmaline vs amethyst: how do you tell them apart?
Tourmaline shows strong pleochroism, a triangular striated prism, and no cleavage, while amethyst is hexagonal, only weakly pleochroic, and has a more violet tone.
Is plum tourmaline the same as rubellite?
They are closely related elbaite tourmalines; rubellite is pink to red, while plum tourmaline leans more purple-red, like the color of a plum.