Pinpoint — The Smallest Diamond Inclusion
Pinpoint — The Smallest Diamond Inclusion
A minute crystal less than 0.02 mm across, the most common inclusion type in fine diamonds
A pinpoint is a minute crystal inclusion in a diamond, typically less than 0.02 mm across, appearing as a single tiny dot under 10x magnification. Pinpoints are among the most common inclusion types in diamonds and coloured gemstones and represent the boundary at which laboratory clarity grading shifts from feature-by-feature plotting to descriptive cloud designation. A diamond whose only internal characteristics are isolated pinpoints will typically grade Very Slightly Included (VS) or higher; an accumulation of pinpoints into a cloud is the principal mechanism by which clarity grades drop into Slightly Included (SI) territory in otherwise clean stones.
Composition and origin
Pinpoints in natural diamonds are typically tiny crystals of accessory minerals trapped during diamond growth in the deep mantle. Common pinpoint compositions include olivine, chrome diopside, garnet, sulphide minerals (pyrrhotite, pentlandite), and other diamond-associated phases identified in microscopic and Raman-spectroscopic studies of natural diamond inclusions. The precise mineralogy of any given pinpoint is rarely diagnostic at the size scale at which the feature is visible, and laboratory grading does not generally identify the host mineralogy.
In synthetic diamonds, pinpoint inclusions can be characteristic markers of growth method. CVD synthetic diamonds frequently display pinpoint clouds aligned along growth layers — a diagnostic feature distinct from the random distribution of pinpoints in natural diamonds. HPHT synthetic diamonds may contain metallic flux pinpoints from the growth solvent, also distinct from natural pinpoints in their composition and distribution. The recognition of these characteristic features is one of the principal techniques laboratories use to distinguish synthetic from natural material.
In clarity grading
Pinpoints are reported on GIA, AGS, AGL, and other laboratory clarity-graded reports through plotting on the diamond clarity diagram and, where pinpoints are sufficiently numerous, through the descriptive note cloud with or without a plot. Isolated pinpoints, particularly those located near the table or under the crown facets, may be the grade-setting feature in stones graded at VVS1 (one or two minute pinpoints in well-positioned locations) through SI2 (a more extensive collection of pinpoints producing a noticeable cloud).
The trade convention for pinpoint reporting on GIA reports is that individual pinpoints below approximately 0.02 mm are not plotted as separate symbols on the clarity diagram unless they are the grade-setting feature; instead, a comment such as pinpoints are not shown is added to the report. Larger pinpoints, recognised individual crystals, and clouds composed of distinguishable pinpoints are plotted with the appropriate symbol.
Practical implications
For buyers of fine diamonds, a clarity grade of VS or higher with pinpoints as the grade-setting feature is generally a more desirable outcome than the same grade with feathers, crystals, or other more visible inclusion types. Pinpoints at this size are essentially invisible to the naked eye and rarely affect the optical performance of a stone. The trade convention is that pinpoint-only inclusion suites at VS clarity represent very high quality material, often preferred to internally flawless stones at marginal price differentials.
For coloured gemstones, pinpoints in corundum, beryl, and other species similarly represent a generally favourable inclusion type. The pinpoint inclusions characteristic of marble-hosted Burmese sapphires and rubies (calcite microcrystals, short rutile silk fragments) are part of the classical inclusion suite of premium origin material and are read by dealers and laboratories as positive indicators of natural origin and Mogok-belt provenance.