What is dumortierite? The charm of boron mineral that harbors deep indigo and how to choose it
What is dumortierite? The charm of boron mineral that harbors deep indigo and how to choose it
A rare blue-blue stone that is neither lapis lazuli nor sodalite.
A specialist buyer will explain both the faceted and quartz twin forms.
Sai
Supervision: Kozo Saito (Selby EC/SNS/Ruth/Production Department Manager) A specialist buyer who directly inspects mining areas in Brazil and Namibia and has earned the trust of local contractors to the point where they call him "Lethal Weapon." As the only company in the Komehei Group specializing in jewelry, we supervise everything from selection of rough stones to production.
1. What is dumortierite? Conclusion: Indigo-blue boron-containing mineral
Conclusion:Dumortierite has the chemical formula (Al,Fe³⁺)₇(BO₃)(SiO₄)₃O₃ represented byBoron-containing aluminum silicate mineral. It is a rare stone with a deep blue to indigo blue color and a hardness of 7 on the Mohs scale, making it durable for everyday use.
1-1. Name derived from French paleontologist Dumortier
This mineral was discovered and described in the Rhône department of France in 1881 by a 19th century French paleontologist.Eugène DumortierIt was named in honor of. The historicity of the name itself is proof that the mineral has been loved for a long time.
1-2. Chemical composition and characteristics of orthorhombic system
dumortierite isorthorhombic systemIt belongs to , and forms fibrous to columnar crystals. The main ingredients are boron (B) and aluminum (Al), with trace amounts of iron (Fe) and titanium (Ti) creating a unique deep blue color. The figure below is a schematic diagram of its crystal structure.
1-3. Mohs hardness 7, relatively easy to handle rare stone
Mohs hardness is7〜8.5This is equivalent to or better than quartz. Although it is a rare stone, it can also be used as an everyday ring or pendant, which is why it is popular among collectors.
2. Two forms: faceted crystals and quartz twin morcellite
Dumortierite distributed in the market is largelytwo formsIt is divided into Since the price, rarity, and appearance vary greatly, it is essential to understand them before purchasing.
① Facet cut product (single crystal)
A transparent single crystal part cut into facets.extremely rareThose over 1 ct are prized worldwide.
Main production area: Minas Gerais, Brazil, Namibia
② Quartz twin dumortierite
Dumortierite is encapsulated in fibrous crystals (quartz).Unique blue inclusion patternis attractive.
Main production area: Bahia, Brazil
2-1. Single crystal facet cut product (extremely rare)
The annual distribution of transparent single crystals is limited worldwide, and they are traded as one-of-a-kind items in the collector market. It is highly pleochroic, and the color changes dramatically depending on the direction of the table surface, so the cutter's technique has a large effect on quality.
2-2. “Quartz Twin Dumortierite” encapsulated in crystal
Dumortierite in Quartz is a state in which acicular and fibrous dumortierite is incorporated into a quartz host rock. Processed into cabochons and beads,"Blue Quartz"It may also be distributed as.
2-3. Differences in market volume and price range for each product
| Form | Distribution volume | Price range (estimate) | Main uses |
|---|---|---|---|
| faceted crystal | Extremely small | 30,000 to 150,000 yen/ct | Unique items for collectors |
| quartz twin | medium | 3,000-15,000 yen/ct | cabochon jewelry |
| Beads/Rough stones | many | Several hundred yen~/piece | accessories/specimens |
*Price is a guideline based on Selby purchasing results as of June 2026. Varies depending on exchange rate and quality.
3. Differences from lapis lazuli and sodalite
Dumortierite is often confused with lapis lazuli and sodalite, simply because it is a "blue stone." We will sort out the decisive differences in differential diagnosis.
3-1. Differences in chemical composition and coloring mechanism
| Item | dumortierite | lapis lazuli | sodalite |
|---|---|---|---|
| main component | Al₇(BO₃)(SiO₄)₃O₃ | Aggregate of lazurite etc. | Na₈(Al₆Si₆O₂₄)Cl₂ |
| classification | single mineral | Rocks (multiple minerals) | single mineral |
| Cause of color development | Fe-Ti charge transfer | S₃⁻ radical | S₃⁻ radical |
| crystal system | orthorhombic system | — | equiaxed crystal system |
3-2. How to distinguish by specific gravity, hardness, and gloss
| Physical properties | dumortierite | lapis lazuli | sodalite |
|---|---|---|---|
| mohs hardness | 7〜8.5 | 5〜6 | 5.5〜6 |
| specific gravity | 3.21〜3.41 | 2.7〜2.9 | 2.27〜2.33 |
| luster | Glass~silk luster | resin ~ earthy | glass gloss |
| pyrite | Does not include | With golden spots | Does not include |
Tips to tell the difference:If there is pyrite (golden spots), it is lapis lazuli. If it has a hardness of 7 or higher and has fibrous blue inclusions, it is dumortierite (quartzine). If you remember that if the specific gravity is extremely light, it's sodalite, you won't get confused on site.
3-3. Descriptions in identification documents and reliable identification laboratories
On the identification document, it will be written as "Dumortierite" or "Quartz with Dumortierite Inclusions." Accurate identification is possible at major domestic and international identification organizations such as GIA, Central Gem Laboratory (CGL), and AGT Gem Laboratory.
🔗 Related spoke articles (blue/similar rare stones)
4. Main production areas
4-1. Made in Brazil: High quality production area in Minas Gerais
Minas Gerais, Brazil, is the world's leading producer of facetable single crystals. The state of Bahia is a major producer of quartzite, and the raw stone has beautiful fiber patterns in the host rock.
4-2. From Namibia: deep indigo blue
The rough stones produced around Kneen Province in Namibia areRich indigo to royal blueIt is popular for its high color saturation. Saito will inspect local mines in 2023 and establish a direct purchasing route.
4-3. Characteristics of Madagascar, Sri Lanka, Norway, etc.
Madagascar produces individuals with a strong purple tinge, Sri Lanka produces small but highly saturated individuals, and Norway produces individuals that have historical value as their place of origin. The uniqueness of each region makes it highly collectable.
5. Color mechanism and pleochroism
5-1. Color development of charge transfer due to iron and titanium
The blue color of dumortierite comes from the crystals.Fe²⁺ → Ti⁴⁺ charge transfer transition (IVCT)It originates from The mechanism is the same as that of sapphire blue, but the color is unique because it has boron in its skeleton.Indigo blueIt will be.
5-2. How strong pleochroism (blue to reddish purple to brown) appears
This mineral isStrong trichroism (pleochroism)The appearance changes as shown below depending on the direction of the crystal axis.
5-3. Differences in color appearance depending on cutting direction
the cutter on the table surfaceα axis (darkest blue)The standard is to match. Even in the case of quartz twin products, the saturation of blue can be maximized by designing the dome surface of the cabochon by paying attention to the flow direction of the inner fibers.
Selby rare stone loose list
You can view rare blue stones including dumortierite by region of origin, cut, and budget.
See colored stone loose →6. How to choose | 4 perspectives to avoid failure
6-1. Color depth and uniformity
The first evaluation axis iscolor. The ideal is an individual whose ``ink-like deep indigo'' spreads evenly under natural light. Individuals that are too pale will be less rare, and individuals that are too dark will look black, so avoid them.
6-2. Location and size of inclusions
Faceted products should have few inclusions, and quartz twin products should have few inclusions.“Is the pattern itself beautiful?”We focus on The balance of flow, shading, and density of the pattern determines its value as a one-of-a-kind item.
6-3. Faceted vs. quartz twin, which one is better?
Who are faceted products suitable for?
・I want to enjoy transparency and pleochroism
・I want to own it as a collection
・Focus on the rarity of one-of-a-kind items
Which direction is the quartz twin facing?
・I want to enjoy unique patterns
・I want to make large jewelry
・I want to enjoy the blue color on a budget
6-4. Balance between size and budget
A realistic option for faceted products is around 1ct. Quartz twin products are large in size of 5 to 20 carats and are suitable for pendants. Deciding on your budget and purpose first will make your selection much smoother.
7. How to treat it as jewelry
7-1. Hardness 7, suitable for daily use
Mohs hardness of 7 is equivalent to crystal. Although it can withstand ring use, it will be damaged if it rubs against diamonds (hardness 10), so a stand-alone case is recommended when storing it.
7-2. Suitable for both rings and pendants
Faceted productsbezel settingThe best way is to bring out the deep blue. Quartz twin products make use of cabochonsCovering ring claspor show the inner pattern through.open backis also popular.
7-3. Frame design proposal by Saito, production department manager
Suggestion from Saito:``The rich indigo from Namibia is better than the white frame of Pt900.K18 yellow goldMy preference is to tone down the blue. The quartz twin piece has an open back made of 18K white gold, and when the light is removed to reveal the pattern, it creates a unique presence. ”
8. Dumortierite imported directly from Selby
8-1. Purchase routes from both Brazil and Namibia
Selby isKomehei Group's only jewelry specialty companyAs such, we have direct purchasing routes to both Minas Gerais, Brazil and Kunin, Namibia. We select stones locally from the rough stage, without going through an intermediate trading company.
8-2. Takazo Saito’s on-site visit episodes and selection criteria
Saito, affectionately nicknamed ``Lethal Weapon'' by local dealers, visits mining areas in Namibia, Brazil multiple times a year.“I never buy rough stones without seeing them locally.”Based on this philosophy, we select each piece based on the three axes of saturation, transparency, and suitability for cutting.
8-3. Long-term peace of mind with Komehei Group's purchase guarantee
The loose jewelry purchased at Selby is from the Komehyo Group.Purchase networkResale is possible through. We respond to "future value fluctuations" unique to rare stones using the group's current market prices.
9. Frequently asked questions (FAQ)
What is different from lapis lazuli?
Lapis lazuli is an aggregate (rock) of multiple minerals, and is characterized by its blue color due to golden pyrite spots and S₃⁻ radicals. Dumortierite is a single mineral, does not contain pyrite, exhibits a blue-blue color due to Fe-Ti charge transfer, and has a high hardness of 7 or higher.
Why is quartz twin morcellite cheaper?
While single-crystal facetable raw stones are extremely rare, quartz crystals (quartz twins) are produced in relatively large quantities and are easy to process, so the market price is about 1/10 to 1/30 of faceted products.
Will the color change when exposed to sunlight?
Because the color is caused by charge transfer (IVCT), it is a mineral that does not easily fade under normal everyday light. However, prolonged exposure to strong UV rays is not recommended. When storing it, it is sufficient to store it in a jewelry box.
10. Why Dumortierite in Selby?
10-1. Professional identification ability to prevent confusion with similar stones
Rare blue stones are a genre where identification errors are likely to occur. Selby uses its unique identification flow and external identification laboratory toMatch between description and realityWe are thorough.
10-2. One-stop consultation for jewelry production
We provide an integrated in-house system that covers everything from loose selection to design proposals, production, and after-sales maintenance.Saito, head of production departmentwill provide direct consultation.
10-3. Compare other blue rare stones in the rare stone loose list
In addition to dumortierite, we also carry a wide range of rare blue stones such as euclase, kyanite, and benitoite. You can choose the most suitable one after comparing and considering.
📚 Parent article/spec comparison
"Rare blue stones" from the perspective of a professional buyer.
Takazo Saito carefully selects and delivers Dumortierite directly imported from Brazil and Namibia.
One-of-a-kind items may be sold out as soon as they arrive.
Sai
Supervision: Kozo Saito (Selby EC/SNS/Ruth/Production Department Manager) We directly inspect mining areas around the world, including Brazil, Namibia, and Madagascar, and as the Komehei Group's only jewelry specialist company, we supervise everything from the selection of rare stones to production and after-sales service. Gaining the trust of local contractors with the nickname "Lethal Weapon."