Facetting.
FACETTING.COM · A CATALOGUE FOR THE TRADE
REFERENCE · 5 MIN READ

Gemstone hardness and cutting difficulty overview.

A neutral reference on the Mohs scale, fracture toughness, and the species-specific factors that bear on lapidary workflow.

Contents · general reference
01Overview of lapidary equipment categories8 MIN02What is a faceting machine?4 MIN03Types of faceting machines5 MIN04Types of laps used in gem cutting6 MIN05Understanding lap grits and progressions6 MIN06Introduction to dops and transfer systems5 MIN07Overview of common rough gemstone materials8 MIN08Gemstone hardness and cutting difficulty overview5 MIN09Polishing compounds overview5 MIN10Measurement instruments in lapidary and gemmology5 MIN
Contents · gemstone overviews
G01Corundum rough overview5 MING02Quartz rough overview5 MING03Beryl rough overview5 MING04Garnet rough overview5 MING05Tourmaline rough overview5 MING06Topaz rough overview5 MING07Peridot rough overview4 MING08Spinel rough overview4 MING09Chrysoberyl rough overview4 MING10Zircon rough overview4 MIN
About this entry

This reference entry describes categories of equipment and material encountered in the lapidary trade. Definitions, typical specifications, and usage ranges are drawn from published manufacturer documentation and standard glossaries. It does not constitute instruction, training, or professional advice. Readers interested in acquiring equipment should consult a qualified retailer or craftsperson.

Where a manufacturer or product name appears in the text, it is illustrative. Links to retailer listings elsewhere on the site are affiliate links and are disclosed as such.

Mohs scale

The Mohs scale of mineral hardness ranks ten reference minerals on a relative-scratch basis. The scale is ordinal, not linear: corundum (Mohs 9) is several times harder than topaz (Mohs 8) by quantitative measure. The scale is a coarse but practical predictor of the abrasive grit and lap bond appropriate for a given species.

Common gemstone landmarks:

  • 6 — feldspar group; opal
  • 6.5 — peridot, demantoid garnet
  • 7 — quartz family; tourmaline (lower end)
  • 7.5 — beryl family (lower end); almandine garnet
  • 8 — topaz, spinel
  • 8.5 — chrysoberyl
  • 9 — corundum (ruby, sapphire)
  • 10 — diamond

Hardness vs. toughness

Hardness — resistance to scratching — is distinct from toughness, the resistance to fracture under impact. Diamond is the hardest natural mineral but is comparatively low in toughness because of its perfect octahedral cleavage. Jadeite is much softer than topaz but tougher because of its interlocking microcrystalline structure.

Lapidary work intersects both properties. Hardness governs the cutting and polishing stages; toughness governs how aggressively the cutter can advance through cutting and how stable the dop transfer is.

Cleavage

Cleavage planes are oriented zones of weakness in the crystal lattice. Topaz has a single perfect basal cleavage that bears directly on faceting; the cutter orients the stone to avoid placing a cleavage plane parallel to the quill axis at high angles. Fluorite has four cleavage planes; corundum has none. Manufacturer cutting guidance for cleavage-prone species typically appears in catalog data.

Heat sensitivity

Some species are thermally sensitive. Tanzanite, kunzite, and some tourmalines can fracture if subjected to rapid temperature changes during dopping. The choice between hot-melt wax and cold-cure epoxy is informed by heat sensitivity.

Implications for grit selection

Harder species tolerate coarser cutting grits without surface damage. Corundum is conventionally cut with a 360 mesh starting lap; quartz responds well to a 600 mesh start; opal is typically not cut with diamond at all but with progressively finer silicon carbide. The relationship between hardness and grit choice is not strict and is documented in published faceting guidance from species-specific sources.

© MMXXVI · FACETTING.COM