Custom cushion-cut clinohumite, 3.31 cts, 9 x 9 mm, Pamir Mountains, Tajikistan. © The Gem Trader. Used with permission.
Clinohumites and chondrodites can make beautiful gemstones with rich colors, but these members of the humite mineral group are rare and little known to the gem buying public.
| Data | Value |
|---|---|
| Name | Humite |
| Colors | Slightly brownish yellow, yellow, deep orange, brown, white. Chondrodites may be red. Clinohumites may very rarely show colors such as reddish orange or yellow-green. |
| Fracture | Subconchoidal, uneven |
| Hardness | 6-6.5 |
| Cleavage | Poor |
| Crystallography | Varies by group member. See "Identifying Characteristics" below. |
| Refractive Index | Varies by group member, 1.563-1.674. See "Identifying Characteristics" below. |
| Birefringence | Varies by group member, 0.026-0.041. See "Identifying Characteristics" below. |
| Dispersion | 0.021 (Clinohumite) |
| Luminescence | Usually inert in SW, sometimes yellow, orange-yellow, or golden yellow; dull orange to brownish orange in LW. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Pleochroism | See "Identifying Characteristics" below. |
| Optics | Biaxial +. See "Identifying Characteristics" below. |
| Optic Sign | Biaxial + |
| Luster | Vitreous |
| Specific Gravity | 3.15-3.35. See table below. |
| Transparency | Translucent to transparent |
| Formula | See “Identifying Characteristics” below. |
| Etymology | Humite is named after Sir Abraham Hume, an English collector of gems and minerals. Clinohumite refers to its monoclinic crystal structure. Chondrodite comes from the Greek chondros for “grain,” alluding to the mineral's granular nature. Norbergite is named after Norberg, Sweden, where it was discovered. |
| Occurrence | In contact zones in limestone or dolomite. Rarely in alkaline rocks of igneous origin. This paragenesis is true for all members of the humite group. |
| Inclusions | Two-phase inclusions, fingerprints, growth lines. Clinohumites from Tanzania may contain needle-like inclusions. |
This vug holds a 5mm yellow, gem-quality humite crystal from the type locality, Monte Somma, Vesuvius, Naples Province, Campania, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.
Humite lends its name to a mineral group as well as a series within that group. The humite series includes norbergite, chondrodite, humite, and clinohumite.
All these minerals are rare, but chondrodite is the most abundant member of this series. This material has very rich colors and a durability good enough for jewelry use, and cutting poses no great difficulty. Unfortunately, rough suitable for cutting is virtually unobtainable and could only yield tiny gems, so faceted chondrodites are almost unknown. Norbergite and humite itself also face a similar situation.
Cherry red chondrodites with gray-green clinochlores, 7.5 x 7.0 x 5.5 cm (specimen), 1.4 cm (chondrodites), Kokscha Valley, Badakshan Province, Afghanistan. © Rob Lavinsky, www.iRocks.com. Used with permission.
Although scarcer, clinohumites are more commonly faceted than their fellow series members. Gem-quality, transparent, slightly brownish yellow to reddish orange crystals have been found in the Pamir Mountains, primarily in what is now Tajikistan. This material can yield beautiful, flawless gems.
Oval-cut clinohumite, 7.45 cts, 13.1 x 11.1 x 7.9 mm, Pamir Mountains, Afghanistan. © ARK Rare Gems. Used with permission.
Since humite series minerals have similar properties, they can be easily confused. Their compositions are related in a very distinctive way.
The presence of titanium dioxide (TiO2) in humite and clinohumite strongly affects their optical properties.
|
Norbergite |
Chondrodite |
Humite |
Clinohumite |
Clinohumite (Tajikistan) | |
| Crystallography | orthorhombic | monoclinic | orthorhombic | monoclinic | |
| Colors | yellowish tan | brown, yellow, red | yellow, deep orange | brown, yellow, orange, white | |
| Hardness | 6.5 | 6.5 | 6 | 6 | |
| Specific Gravity | 3.15-3.18 | 3.16-3.26 | 3.20-3.32 | 3.17-3.35 | |
| Optics | |||||
| α | 1.563-1.567 | 1.592-1.615 | 1.607-1.643 | 1.629-1.638 | 1.631 |
| β | 1.567-1.579 | 1.602-1.627 | 1.639-1.675 | 1.662-1.643 | 1.639-1.647 |
| γ | 1.590-1.593 | 1.621-1.646 | 1.639-1.675 | 1.662-1.674 | 1.668 |
| 2V | 44-50° | 71-85° | 65-84° | 73-76° | |
| Birefringence | 0.026-0.027 | 0.028-0.034 | 0.029-0.031 | 0.028-0.041 | 0.037 |
| Pleochroism | |||||
| α | pale yellow | very pale yellow/brownish yellow | yellow | golden yellow/ deep reddish yellow | |
| β | very pale yellow | colorless/ yellowish green | colorless/ pale yellow | pale yellow/orange yellow | |
| γ | colorless | colorless/pale green | colorless/ pale yellow | pale yellow/orange yellow |
All members of this group have poor cleavage, vitreous luster, and a biaxial (+) optic character. Typically, they show yellowish brown colors. Clinohumites from China have been found with reddish orange color, and some clinohumites from Tanzania show yellow-green colors.
Clinohumite fluoresces slightly orangey yellow in shortwave (SW) ultraviolet light (UV). Humite may fluoresce slightly yellow in SW UV. Chondrodite may fluoresce yellow in SW UV and slightly orange in longwave (LW) UV. Norbergite may fluoresce bright yellow to golden yellow in SW UV.
This orange, gem-quality norbergite crystal on a calcite matrix fluoresces golden yellow under ultraviolet light. 4.2 x 3.6 x 2.8 cm (calcite), 9 mm (norbergite), Mogok Township, Pyin-Oo-Lwin District, Mandalay Division, Myanmar. © Rob Lavinsky, www.iRocks.com. Used with permission.
Scientists have synthesized the humite series members using a variety of methods. However, there’s no known jewelry use for this lab-created material.
None known.
Clinohumite rough. (The coin is 1 Pakistani rupee, 20 mm in diameter). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Although rare, humite series members occur across the globe.
The most well-known source for gem-quality clinohumite is Tajikistan, in the Pamir Mountains. Russia also produces gem-quality clinohumite in the Lake Baikal and Taymyr regions.
Tilly Foster Mine in Brewster, New York produces fine crystals of reddish brown, gemmy chondrodite, associated with humite and clinohumite. This is the principal source of most gem-quality chondrodite.
Chondrodite: Tilly Foster Mine, Brewster, New York (gem, around 2 cts; rough, around 1” long). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Afghanistan, China, and Tanzania produce gem-quality clinohumite and chondrodite.
Other notable clinohumite sources include the following:
Norberg, Sweden and, in the United States, Franklin, New Jersey and Orange County, New York produce norbergite.
Myanmar produces norbergite and chondrodite.
Vietnam yields humite, clinohumite, and chondrodite.
Notable humite sources include the following:
Oval-cut chondrodite, 2.20 cts, 9.0 x 7.1 x 4.4 mm, Tanzania. © ARK Rare Gems. Used with permission.
Cut humite series members were long known as small gems, usually from 1 to 3 carats in size. Crystals tended to be dark and filled with inclusions and fractures, so larger cut gems were extremely rare.
The discovery of gem-quality clinohumites since the 1980s has yielded material for larger gemstones. Faceted Tajikistani clinohumites of 36.56 cts and even 84.23 cts have been documented.
18k white gold ring with round brilliant-cut diamonds, about 1.50 ctw, and an oval modified brilliant-cut clinohumite, about 10.36 cts. Photo courtesy of liveauctioneers.com and Hindman.
Although clinohumites and chondrodites can make durable gemstones, they still have a hardness of 6 and 6.5, respectively, less than that of household dust. To prevent scratches, use protective settings and reserve any jewelry pieces for occasional wear.
Since these gems may have many inclusions, including two-phase inclusions, don’t place them in ultrasonic or other mechanical cleaning systems. Clean them only with a soft brush, mild detergent, and warm water.
Consult our gemstone jewelry cleaning guide for more recommendations.
Clinohumite: Tajikistan (1.52). Photo © Joel E. Arem, PhD, FGA. Used with permission.
IGS Newsletter