If you or your business is involved in buying or selling diamonds (or if you are just somebody who is curious about diamonds ), you might have noticed something weird and annoying - some HPHT (High-Pressure High Temperature) diamonds are coming up as Moissanite on a few diamond testers.
Sounds confusing, right?
This increasing concern is giving rise to identification issues for jewelers, gemologists, and consumers.
So, what’s going on?
To understand this, we have to examine what HPHT diamonds are in reality. These are genuine diamonds—not simulants or synthetics—made or treated under intense pressure and heat to enhance clarity or color. The twist is the HPHT treatment can change the diamond's conductivity, and on occasion, the diamond may fool diamond testers (like the ones based on electrical signals) and be identified as Moissanite, a separate material with thermal characteristics that are similar but optical and chemical properties that are different from those of diamonds.
In this post, we’ll break down:
- Why HPHT diamonds are misidentified as Moissanite
- Which diamond testers are most affected
- How can you accurately identify and test HPHT diamonds
Let’s clear up the confusion!
Does the Lab Diamond Test as Moissanite?
AdobeStock/Johannes
Both jewelry professionals and customers are often surprised to hear that not all lab-grown diamonds test negative as Moissanite and that some, in fact, do test positive despite being real diamonds with an identical carbon lattice structure to natural diamonds.
This is mainly seen in the HPHT of diamonds, and they may even be semiconductive in nature as a result of containing boron impurities that are added during growth. Here’s why:
Understanding Diamond and Moissanite Tester Principles
Most diamond testers available in retail jewelry stores rely on two core principles:
Thermal Conductivity
- Diamonds have extremely high thermal conductivity; heat moves rapidly through them.
- Moissanite also has a very high thermal conductivity, though marginally lower than lab diamond.
- Materials like cubic zirconia or glass conduct heat much more slowly, making them easy to distinguish.
Electrical Conductivity
- Natural diamonds are excellent electrical insulators compared to Lab diamonds; they do not conduct electricity.
- Moissanite is electrically conductive due to its silicon carbide composition.
- Many modern testers measure electrical conductivity to rule out Moissanite quickly.
In theory, these two readings together allow testers to identify whether a stone is a diamond, Moissanite, or another simulant. But HPHT diamonds complicate this picture.
Related: The Difference Between a Natural Diamond and Lab-Grown Diamond
Why HPHT Lab Diamonds Trigger Moissanite Readings
HPHT synthesis uses a growth cell filled with metallic flux, like nickel or iron. This flux melts the carbon and makes it easier for a diamond crystal to form. Even very low levels, just parts per million, can affect the diamond in a big way. A pure diamond does not let electricity pass. Once it contains these metals, though, it becomes a semiconductor and starts to conduct electricity.
This electrical conductivity is exactly what Moissanite testers are designed to detect.
In other words:
- An HPHT diamond containing boron conducts electricity.
- A Moissanite also conducts electricity.
- A tester reads conductivity and flags the stone as Moissanite, even though the diamond is genuine.
This is why lab-grown diamonds, especially Type IIb HPHT diamonds, are often flagged incorrectly.
Types of Diamond Testers and Their Limitations
The three main categories of diamond testers, along with their operational principles and specific shortcomings:
1. Thermal Conductivity Testers
These are testers that depend on the fact that the diamond is the most thermally conductive gemstone. The probe is used to check the rate at which heat is dispersed in the material when it touches the stone.
A heated metal tip touches the gem. The instrument calculates heat loss, comparing it to reference values for diamonds. If the stone quickly conducts heat away, the device signals a “diamond.”
Limitations
The thermal conductivity of Moissanite is nearly as high as diamond, which means these testers cannot reliably distinguish between the two.
- Stones like synthetic Moissanite (silicon carbide) and HPHT diamonds will often trigger the same readings.
- External factors, such as the stone’s temperature, mounting, and contamination, can affect accuracy.
Such instruments successfully distinguish diamonds and low-conductivity impersonators; they cannot serve as standalone tools to detect Moissanite or identify lab-grown diamonds.
2. Electrical Conductivity Testers
Electrical conductivity testers were created to address the weaknesses of thermal devices. Moissanite is an electric conductor, but most natural diamonds are not.
The probe passes a small electrical charge onto the stone surface. In case the material is electricity-conducting, the device refers to it as Moissanite.
Limitations
Type IIb HPHT diamonds contain boron impurities, making them semiconductive. As a result, these genuine lab-grown diamonds can test positive as Moissanite, triggering false identifications.
- Some natural blue diamonds are also Type IIb, compounding the risk of error.
- Surface contamination, such as oils, moisture, or residues, can interfere with conductivity readings.
Electrical testers are more accurate than thermal testers for screening out most Moissanite. However, they are completely unreliable for determining if a conductive stone is HPHT diamond or Moissanite, and should never be used as the sole basis for identification.
3. Combined Multi-Function Testers
Many modern devices integrate both thermal and electrical conductivity modes to provide a more comprehensive assessment. Examples include the Presidium Multi Tester III and the Gemoro Testerossa.
These testers first measure thermal conductivity to identify stones likely to be diamond or Moissanite. They then apply an electrical test to differentiate Moissanite based on conductivity.
Limitations
- Even multi-function devices cannot conclusively separate Type IIb HPHT diamonds from Moissanite because both conduct heat and electricity in overlapping ranges.
- They rely on preset thresholds that do not account for the complex semiconductor behavior of boron-doped diamonds.
- Variations in battery power, probe calibration, and operator technique can create inconsistent results.
Many people use a multi-function tester to screen diamonds fast, but this tool doesn’t give a final answer about authenticity. It falls short when you need to verify high-value lab-created diamonds. For accurate results, skilled gemologists rely on deeper analysis.
Read in Details: Can Lab-Grown Diamonds Pass as Real on a Diamond Tester?
Professional Identification Methods to Differentiate Between HPHT Diamonds & Moissanite
The identification of HPHT diamonds from HPHT Diamonds follows the three main testing processes.
| 🧪 Advanced Gem Testing | 🔍 Visual Inspection |
🛠️ Professional Equipment |
| Photoluminescence & Raman – Detect boron & diamond structure | Inclusions & Double Refraction – Moissanite shows facet doubling | DiamondView Imaging – Reveals lab-grown growth patterns |
| UV Fluorescence & FTIR – Highlight HPHT traits | Growth Patterns – Cuboid sectors in HPHT diamonds |
GIA/IGI Certification – Confirms identity & origin |
| Spectroscopy – Clear material fingerprint | Facet Analysis – Moissanite vs. diamond clarity |
Multi-Mode Testers – Extra verification, but not conclusive |
FAQs
Can HPHT diamonds be detected without lab equipment?
Magnification is handy when you want to catch double refraction. That can help rule out Moissanite. Sometimes, you might see metallic bits inside, and that points to HPHT growth. Still, no approach besides expert gem tools can say for sure if a diamond is HPHT. Pocket testers only give you a first look and nothing more.
How much does professional diamond identification cost?
A simple lab report from a gemologist usually costs around $75 to $150 in most places. Detailed grading and origin papers from GIA or IGI start near $150 and can go up to $500. The final price depends on how big the diamond is and how deep the analysis goes.
The Bottom Line
While diamond testers are valuable tools in the jewelry industry, they are designed only as preliminary screening devices, not as definitive instruments. No portable tester—thermal, electrical, or combined- can fully overcome the problem of HPHT lab diamonds mimicking Moissanite’s conductive properties.
To ensure an accurate identification:
- Always request a professional gemological report, like GIA or IGI.
- Use advanced analytical methods to confirm the origin.
- Be careful when purchasing high-value stones; test only with handheld devices.
The technical limitations are as important for both jewelers and buyers to make informed decisions and avoid misidentification.
If you have more questions about HPHT diamonds, testing accuracy, or are exploring custom lab-grown diamond jewelry, feel free to call (213) 306-7211 or book a quick appointment with one of our lab diamond specialists.
