What Is a Type IIa Diamond, and Why Are Most CVD Diamonds Type IIa?
Type IIa is a rare, chemically pure kind of diamond, under 2% of natural diamonds, yet most CVD lab-grown diamonds belong to it. What diamond types mean and why it matters.
Scientists sort diamonds into "types" according to which trace elements they contain, mainly nitrogen and boron. One type, IIa, is rare and chemically very pure in nature, and includes many of the most famous diamonds in history. It is also the type most CVD lab-grown diamonds belong to. Here is what that means.
Diamond types, simply
Nitrogen is the most common impurity in diamond. How much there is, and how its atoms are arranged, affects colour and how a diamond absorbs light. Gemmologists use spectroscopy to classify diamonds into four types:
- Type Ia: nitrogen atoms in clusters. About 98% of natural diamonds; often slightly yellow.
- Type Ib: isolated nitrogen atoms. Rare in nature; intense yellow "canary" colours.
- Type IIa: virtually no nitrogen. Under 2% of natural diamonds; can be exceptionally white.
- Type IIb: boron instead of nitrogen. Extremely rare; blue and conduct electricity.
Famous Type IIa diamonds
Several of the world's most celebrated large diamonds are Type IIa, including the Cullinan, the largest gem-quality rough diamond ever found, and the Koh-i-Noor. Their purity is part of why they are so prized.
Why most CVD diamonds are Type IIa
CVD diamonds grow from a carefully controlled gas mix in a vacuum chamber, where growers can keep nitrogen very low. The result is usually Type IIa diamond. HPHT diamonds can also be grown as Type IIa when growers remove nitrogen during growth, while some HPHT stones are Type Ib or IIb.
Does Type IIa make a diamond look better?
Not by itself. A Type IIa diamond can be colourless, but it can also be brownish (often treated to remove the colour) or contain inclusions. A well-cut Type Ia natural diamond can look just as white and bright. Treat diamond type as an interesting scientific fact rather than a quality grade.
How labs use diamond type
Because Type IIa is rare in nature and common in CVD growth, laboratories pay special attention to IIa stones when screening for lab-grown origin. It is one of several clues that, together, allow a lab to state origin with certainty.
How diamond type is measured
Labs determine type with infrared spectroscopy, which shows whether nitrogen is present and how its atoms are arranged. There is also a simpler screening clue: type II diamonds let short-wave ultraviolet light pass through them, while most type Ia diamonds block it. Many screening devices use this to sort diamonds quickly, sending any type II stone for full laboratory testing.
Type IIb: the blue exception
Type IIb diamonds contain boron, which makes them blue and allows them to conduct electricity, something no other diamond does. The famous Hope Diamond is type IIb. Lab-grown blue diamonds are made the same way, by adding boron during growth. Because they conduct electricity, blue diamonds can confuse the electrical testers used to spot moissanite, another reason a proper lab report matters.
Type and treatment
In 1999 the trade learned that some brown type IIa natural diamonds could be turned colourless by HPHT treatment. Since then, labs examine colourless type IIa stones especially carefully, natural or lab-grown, to identify both origin and any treatment. For buyers, it is another reason to insist on an independent report that states both.
CVD diamonds in our pendants
Is a Type IIa diamond rare?
In nature, yes: under 2% of mined diamonds. Among CVD lab-grown diamonds, it is the norm.
Is Type IIa better than Type Ia?
Not necessarily. Type describes chemistry, not quality. Judge a diamond by its grading report and how it looks.
Does a grading report show diamond type?
Some reports mention it, especially for natural Type IIa stones or when it relates to treatment; many do not.
Can a blue diamond fool a moissanite tester?
It can. Type IIb blue diamonds conduct electricity, which some moissanite testers rely on, so a lab report is the reliable answer.
