SI (Coloured) — Slightly Included on a Coloured-Stone Report
SI (Coloured) — Slightly Included on a Coloured-Stone Report
An adapted clarity grade applied to coloured gemstones with reservations
The SI grade — slightly included — is borrowed from diamond clarity nomenclature and is sometimes applied to coloured stones to indicate inclusions that are visible under ten-power magnification but typically not distracting to the unaided eye. Use of SI on coloured-stone documents and dealer descriptions is widespread in the American trade but is not the standard adopted by GIA or by the principal European laboratories, which prefer descriptive language more sensitive to the species-specific clarity expectations of coloured stones.
Why coloured-stone clarity differs from diamond clarity
Diamond clarity grading is a single ordered scale applied uniformly across the species, because clarity expectations for diamond are uniform: the ideal is a colourless, transparent stone with no visible features at ten-power. Coloured stones present a fundamentally different problem. Emerald is expected to carry a network of inclusions and surface-reaching fissures that are part of the species's identity; a flawless emerald would prompt suspicion of synthesis or substitution. Sapphire of fine quality is expected to be largely free of eye-visible inclusions but may carry diagnostic silk and rutile clouds that are positive identifiers of natural origin. Demantoid garnet is sought after specifically for the horsetail inclusion that signals Russian Ural origin. A single SI label cannot convey what a slightly included emerald, sapphire, and demantoid mean as commercial propositions.
GIA's preferred system
GIA's coloured-stone reports use a clarity-type classification that groups species by their expected inclusion behaviour: Type I species (aquamarine, topaz, tanzanite, and others) are normally eye-clean and held to that standard; Type II (most ruby and sapphire, garnet) are typically lightly included; Type III (emerald, red beryl, and others) are heavily included as a class. The clarity statement on the report is then descriptive — eye-clean, lightly included, moderately included, heavily included — relative to the type. SI as a discrete letter grade does not appear on GIA reports.
Use in the American trade
Despite the laboratory preference for descriptive language, SI labels persist in dealer parlance, in some American laboratory reports, and in retail point-of-sale documents that lift terminology from diamond practice. Buyers receiving a coloured stone described as SI should ask the seller to specify what the inclusions are, where they are located, whether they are surface-reaching, and what species-appropriate clarity expectation is being applied. The grade by itself is not informative.