Adirondack Garnet Identification Guide

What Adirondack Garnet Looks Like

Adirondack garnet is almandine garnet from the Adirondack Mountains of New York, most famously the giant crystals of the Barton Mine at Gore Mountain. It is New York's state gem and a major industrial abrasive.

• Color: deep brownish-red, purplish-red to wine-red; sometimes nearly black in large masses.
• Luster: vitreous to slightly resinous.
• Transparency: translucent to nearly opaque in big crystals; gem-clear in small fragments.
• Habit: equant isometric crystals, often well-formed rhombic dodecahedra or trapezohedra; Gore Mountain crystals can be enormous (decimeters across) and are typically surrounded by a pale hornblende reaction rim within dark amphibolite/metagabbro host rock.

Step-by-Step Field ID Checklist

1. Check the host rock. Look for large red garnet crystals set in dark green-black amphibolite/gabbroic gneiss, often with a lighter rim around each garnet.
2. Note crystal shape. Rounded, many-faced equant crystals (dodecahedra) with no elongation.
3. Test hardness. Mohs 7–7.5; it scratches glass and quartz easily.
4. Look at fracture. No cleavage; brittle conchoidal-to-uneven fracture (why it makes good abrasive grit).
5. Check the streak. White (the body color does not transfer).
6. Heft. Garnet feels dense (SG ~3.8–4.3 for almandine).

Key Diagnostic Tests

• Hardness: 7–7.5.
• Cleavage: none — diagnostic versus many silicates; fracture is conchoidal and sharp.
• Crystal system: isometric — equant crystals with no preferred direction.
• Specific gravity: high, ~4.0+ for almandine.
• Streak: white.
• Magnetism: iron-rich almandine can be weakly attracted to a strong neodymium magnet.

Common Look-Alikes and How to Tell Them Apart

• Other red garnets (pyrope, rhodolite): visually similar, but Adirondack material is specifically iron-rich almandine; the dark amphibolite host and very large dodecahedral crystals are characteristic. Precise species needs SG/refractive index.
• Ruby/red spinel: much harder distinction by setting; ruby (H 9) and spinel occur in marble, not Adirondack amphibolite, and garnet's lack of cleavage plus isometric form separate it.
• Rhodonite/rhodochrosite: pink-red but much softer (H 6 and 3.5–4) and rhodochrosite fizzes/has cleavage; garnet does neither.
• Red glass/slag: glass lacks crystal faces, has lower hardness, and shows gas bubbles and swirls.

Where Adirondack Garnet Is Found

The signature source is Gore Mountain (Barton Mine), Warren County, New York, where almandine occurs in a coarse garnet amphibolite within high-grade Grenville metamorphic rocks. Garnet also occurs at Ruby Mountain and other Adirondack localities. It forms during high-grade regional metamorphism of iron- and aluminum-rich rocks. Collectors and abrasive miners find it weathering out of, or embedded in, dark hornblende-rich gneiss.