Rock Identifier

Eltyubyuite Identification Guide

A guide to eltyubyuite, an extremely rare chlorine-bearing garnet-group silicate, its appearance, and why field identification requires lab confirmation.

Read the full Eltyubyuite encyclopedia entry →
Eltyubyuite Identification Guide

What It Looks Like

Eltyubyuite is an extremely rare mineral of the wadalite group within the broader garnet supergroup, a calcium-iron chlorosilicate (ideally Ca12Fe10Si4O32Cl6). It occurs as tiny grains and microcrystals, typically pale to greenish or brownish, with a vitreous luster, formed in high-temperature, low-pressure skarn environments. Because it appears only as minute crystals embedded in metamorphosed/altered carbonate rocks, it is effectively a microminral that the average collector will not identify by eye.

Telltale Visual Cues

  • Minute isometric (cubic-system) grains, not large crystals.
  • Pale green to brown, vitreous, transparent to translucent micrograins.
  • Always in a high-temperature skarn/altered-limestone matrix.

Step-by-Step Field-ID Checklist

  1. Recognize the context: pyrometamorphic/skarn rocks (burned, altered carbonate xenoliths) are the only realistic setting.
  2. Use magnification: grains are tiny — a loupe or microscope is essential.
  3. Note the isometric habit: garnet-supergroup minerals are cubic, lacking cleavage.
  4. Estimate hardness: garnet-group silicates are roughly Mohs 6–7.
  5. Do not rely on color alone: it is indistinguishable from several associated phases by eye.
  6. Submit for analysis: positive ID requires EDS/microprobe or X-ray, because of its rarity and Cl content.

Key Diagnostic Tests

  • Mohs hardness: approximately 6–7 (garnet supergroup range).
  • Crystal system: isometric (cubic); no cleavage.
  • Fracture: conchoidal to uneven.
  • Density: relatively high for a silicate (the iron content raises it).
  • Definitive ID: electron microprobe / EDS detecting Ca, Fe, Si, and essential Cl, plus X-ray diffraction matching the wadalite-group structure.
  • Acid: the silicate grains are inert, but the carbonate host fizzes in HCl.

Common Look-Alikes

  • Wadalite: the aluminum-dominant analog; distinguished only by chemistry (Al vs Fe).
  • Andradite garnet: also Ca-Fe and isometric, but lacks essential chlorine; needs chemical analysis to separate.
  • Grossular/hydrogrossular: lighter, Al-rich, no Cl.
  • Other skarn silicates (e.g., melilite, gehlenite): similar settings; require optical/chemical work to tell apart.

Where It Is Found

Eltyubyuite is named for its type locality near the Eltyubyu (Upper Chegem) caldera in Kabardino-Balkaria, North Caucasus, Russia, where it occurs in high-temperature, chlorine-rich skarns within altered carbonate xenoliths in ignimbrite. It is also reported from similar pyrometamorphic environments such as Kerimasi volcano, Tanzania. It remains a rare research mineral rather than a collectible field stone.

Frequently asked questions

What is eltyubyuite?

Eltyubyuite is a very rare chlorine-bearing calcium-iron silicate in the wadalite group of the garnet supergroup. It forms tiny crystals in high-temperature, chlorine-rich skarns.

Can you identify eltyubyuite in the field?

Not reliably. It occurs as minute grains indistinguishable by eye from other skarn silicates and from garnet, so positive identification requires microprobe analysis and X-ray diffraction.

Where is eltyubyuite found?

Its type locality is the Eltyubyu (Upper Chegem) caldera in the North Caucasus, Russia, in altered carbonate xenoliths. Similar material is reported from Kerimasi volcano in Tanzania.

How is eltyubyuite different from andradite garnet?

Both are calcium-iron isometric silicates, but eltyubyuite belongs to the wadalite group and contains essential chlorine, while andradite does not. Telling them apart requires chemical analysis.