Bolivian Amethyst, Ametrine and the Minerals of the Andes

Short answer: Bolivian amethyst means, in practice, one deposit: the Anahí mine in the far southeast of the country, near the Brazilian border. It yields amethyst, citrine and ametrine, the purple and yellow bicolor quartz, and Bolivia is the only commercial source of ametrine. The rest of Bolivia's collector material comes from the Andean tin and silver districts of Potosí and Oruro, which supply cassiterite, vivianite and phosphophyllite crystals.

Where is the Anahí mine, and why was it lost for so long?

Bolivia has two crystal geographies that have almost nothing in common. The high Andes in the west hold the old metal mines. The lowlands in the east, where the country meets Brazil, hold the quartz. The Anahí mine sits in that eastern lowland. According to GIA's February birthstone page, the mine is hidden in the Pantanal wetlands, the seasonally flooded plain that straddles the border.

The mine's story comes with a legend that every dealer repeats, so it helps to know what the sources actually say. GIA's ametrine history relates that a Spanish conquistador found the deposit in the 1600s and received it as a dowry when he married a native princess named Anahí, and that he presented specimens to his queen. GIA's birthstone page identifies her as a princess of the Ayoreo people. Both pages present this as lore, not documented history. What is documented is the gap: the location was lost for more than three centuries, the deposit was rediscovered in the 1960s, and its ametrine began reaching the market again during the 1970s.

The isolation is physical. GIA notes that a clearing near the mine has room only for a small airplane, which goes a long way toward explaining how a gem deposit could disappear from commercial memory for so long. A Gems & Gemology field report adds that the mine has had consistent production since it came under private control in 1990.

What makes Bolivian ametrine two colors?

Ametrine is ordinary quartz, SiO2, with two color zones in one crystal. Minerals.net lists the same core data as any quartz:

The color is the interesting part. The International Gem Society explains that the abrupt color transition reflects slight fluctuations in temperature and pressure while the crystal grew, with iron impurities producing either purple amethyst zones or yellow citrine zones. The underlying chemistry of purple quartz is covered in why amethyst is purple.

The key scientific paper on the deposit is cautious about mechanism. In the 1994 Gems & Gemology study of the Anahí mine, Vasconcelos, Wenk and Rossman concluded from field and laboratory work that the amethyst and citrine combination in Anahí quartz is natural and does not result from laboratory treatment. They attributed the unusual pattern to uncommon geologic conditions during growth, but stated that the crystal chemistry controlling the sector zoning still eluded explanation. That is the honest summary: natural, well documented, not fully understood.

Sector zoning is the visual clue. The color does not fade gradually from tip to base as in a typical amethyst point. Instead, different growth sectors of the same crystal take different colors, so a cross section shows wedges of purple and yellow meeting along fairly sharp lines.

What does the Anahí mine produce, and how much?

The mine is not a one-product operation. GIA's ametrine pages say it also produces natural amethyst and citrine, and the production figures in Gems & Gemology show amethyst is actually the largest share.

The same report records that ametrine remains the most lucrative of the three, and that its share had risen from 20% a decade earlier. GIA's visit found 74 workers active in five tunnels, so this is underground hard-rock mining, not surface digging in gravel. Ore cars bring the quartz-bearing material out, workers wash it on site using local groundwater and presort it, and the rough is then transported to the city of Santa Cruz for cutting and manufacturing.

Two details matter to anyone buying Bolivian quartz. First, the operator has also begun reprocessing old tailings piles to recover pale amethyst, sold in Bolivia under the local name anahíta. Pale lilac Bolivian material is therefore an intended product, not necessarily a low grade. Second, GIA describes the operation as running a mine-to-market chain of custody, controlling extraction, cutting and jewelry production in one sequence. That makes Bolivian ametrine one of the better documented colored stones on the market for provenance, at least for stones that move through that chain.

How is ametrine cut, and what is it called in the trade?

Cutting style tells a buyer a lot about how a stone was meant to be read. According to IGS, when ametrine entered the market in quantity in the 1970s, cutters preferred emerald-cut shapes with a 50/50 color split. Gems & Gemology adds that these early cuts mimicked bicolored tourmaline, but that cutting for an even split wastes much of the rough.

The current approach is different. The Gems & Gemology report describes ametrine cut in round, oval and pear shapes that blend the two colors, giving face-up hues described as peach or deep orangy red, as well as concave-faceted stones such as a 44.23 ct gem faceted in Bolivia. IGS describes the same trend: designs that blend yellow and purple into rosy gold, mauve and champagne, or produce mosaic-like flashes of both colors.

Trade vocabulary varies. IGS lists "amethyst-citrine," "citrine-amethyst," "trystine" and "golden amethyst," and notes the name "Bolivianite," especially inside Bolivia, while advising against it because the name has been applied to other minerals before. Minerals.net accepts "Bolivian Amethyst" simply as a locality term for amethyst from Bolivia.

How can you tell natural Bolivian ametrine from treated or synthetic stones?

This is where a buyer needs realism. IGS states that both heat-treated natural quartz and synthetic ametrine are on the market, and that they match natural ametrine optically and physically, so gemological testing is required. Twinning in quartz used to be read as proof of natural origin, but IGS notes that synthetic quartz can now duplicate it. Minerals.net adds that ametrine can be produced artificially by partial heat treatment of some amethyst or by irradiation.

There is a mitigating factor: Minerals.net observes that ametrine is relatively affordable despite coming from a single locality, so synthetic forms are not in high demand. Fakes are less of a risk than with costlier gems, but they are not absent. For the general logic of heated quartz colors, read the natural vs heated citrine guide, and for lab-grown quartz, the synthetic quartz guide.

Practical checks, none of them conclusive alone:

• Pattern. Natural Anahí stones show sector zones with fairly crisp boundaries. Color that looks painted on, or perfectly uniform halves with no inclusions at all, deserves a lab question.
• Saturation. Minerals.net notes that hydrothermal synthetics often show more vivid, intense color than natural stones. A very saturated, flawless stone at a low price is a reason to ask.
• Locality claims. IGS records that ametrine was first reported from Rio Grande do Sul in Brazil and that small non-commercial occurrences exist in the United States, Canada, India and Mozambique, but that Anahí currently supplies all known gem-quality material. A cut ametrine sold with any other country of origin should be questioned.
• Treatment history. GIA's amethyst page notes heat is the most common treatment for amethyst and can turn some of it yellow. Partial heating of purple quartz is the realistic route to an imitation.

What else comes out of Bolivia?

The Andean side of the country is a separate world. Bolivia's altiplano mining districts were developed for tin and silver, and the veins that carried the ore also produced some of the finest crystals of several species. Geology.com explains that primary cassiterite, the main tin ore, forms in hydrothermal veins associated with granitic intrusions and lists Bolivia among the important primary deposits. The broader process is covered in the hydrothermal veins guide.

• Cassiterite. Minerals.net says Bolivia produces some of the finest cassiterite specimens in abundance, with lustrous and sometimes transparent crystals from Viloco (Araca), Huanuni in Oruro, and Llallagua in Potosí. The IGS cassiterite entry adds that Bolivia produces most of the gem cassiterite known, with the Araca mine yielding yellow, gray, colorless and brownish stones.
• Vivianite. According to Minerals.net, Bolivia has supplied the finest vivianite, transparent dark green crystals with sharp terminations, from the Tomokoni mine near Colavi, the Siglo Veinte mine at Llallagua, and the Morococala and Huanuni mines in Oruro. IGS reports cuttable crystals from Llallagua and Poopó up to 6 inches long.
• Phosphophyllite. The IGS phosphophyllite entry states that Potosí has produced transparent blue-green single crystals up to about 3 by 2 inches, and that only Bolivian phosphophyllite has been faceted. It is a zinc phosphate with hardness 3 to 3.5 and perfect cleavage, a cabinet specimen rather than a stone to handle.

These Andean species sit in a different price class from lowland quartz. A sharp, gemmy vivianite or phosphophyllite from an old Bolivian mine is a serious collector piece, and old labels naming the specific mine add to value.

Buying Bolivian amethyst and ametrine

Start with the label. "Bolivia" on amethyst almost always means Anahí, and a dealer who can say so is giving useful information. For rough or specimen pieces, look for the deposit's sector zoning, check that any yellow zone looks continuous with the crystal rather than like a surface stain, and ask whether a piece has been heated. For cut ametrine, decide whether you want the classic split or a blended cut, and accept that only a lab can rule out synthetic material in a clean, vivid stone. Compare against Brazilian and Uruguayan geode material in the Brazil origin guide and the amethyst guide.

From current stock:

• 79.7 lb Bolivian amethyst is the one piece here with a stated Bolivian origin and a display-scale specimen of about 36 kg; ask for photos of every face and of any cut or repaired surface at that price.
• Amethyst tower from Brazil makes a useful comparison: Brazilian amethyst cut into a point, so you can compare a Brazilian piece with Bolivian material side by side.
• Dream amethyst sphere with chevron purple banding shows how layered purple and white quartz looks when polished, a good reference for reading color zoning in any quartz.
• Pink amethyst is pale, lilac-pink quartz, close in tone to the light material the Anahí operation sells as anahíta.
• Amethyst tumbles are the low-cost way to study purple quartz color and inclusions under a loupe before spending on a cut stone.

Frequently asked questions

Is Bolivian amethyst different from Brazilian amethyst?

The mineral is the same quartz, but the deposits differ. Most Brazilian decor amethyst comes from basalt geodes in the south, while Bolivian amethyst comes from underground tunnels at the Anahí mine near the border, which also yields citrine and bicolor ametrine. A Bolivian label usually means Anahí material.

Is ametrine only found in Bolivia?

Commercially, yes. GIA and Gems & Gemology describe Bolivia as the only commercial source. IGS notes that ametrine was first reported from Rio Grande do Sul in Brazil and that small non-commercial occurrences exist in the United States, Canada, India and Mozambique, but Anahí supplies the known gem material.

Is Bolivian ametrine natural?

The 1994 Gems & Gemology study concluded from field and laboratory work that the color combination in Anahí quartz is natural, not a treatment. Treated and synthetic ametrine also exist, though, and they can match natural stones closely enough that only gemological testing separates them.

What is anahíta?

It is the Bolivian name for pale amethyst from the Anahí mine. Gems & Gemology reported that the operation began reprocessing old tailings piles to recover this light material because it had become popular, so pale lilac Bolivian quartz is a deliberate product.

What collector minerals come from the Bolivian Andes?

The tin and silver districts of Potosí and Oruro supply fine cassiterite from Viloco, Huanuni and Llallagua, dark green vivianite from Tomokoni, Llallagua and Morococala, and rare blue-green phosphophyllite from Potosí. These are cabinet specimens and usually cost more than quartz.

Sources

• GIA, Ametrine Description: https://www.gia.edu/ametrine-description
• GIA, Ametrine History and Lore: https://www.gia.edu/ametrine-history-lore
• GIA, February Birthstone: Amethyst: https://www.gia.edu/birthstones/february-birthstones
• Gems & Gemology (GIA), The Anahí Ametrine Mine, Bolivia, Spring 1994: https://www.gia.edu/gems-gemology/spring-1994-amethyst-citrine-bolivia-vasconcelos
• Gems & Gemology (GIA), Anahí's "New" Ametrine: https://www.gia.edu/gems-gemology/spring-2009-anahi-ametrine-mine
• International Gem Society, Ametrine Value, Price, and Jewelry Information: https://www.gemsociety.org/article/ametrine-jewelry-and-gemstone-information/
• International Gem Society, Cassiterite Value, Price, and Jewelry Information: https://www.gemsociety.org/article/cassiterite-jewelry-and-gemstone-information/
• International Gem Society, Vivianite Value, Price, and Jewelry Information: https://www.gemsociety.org/article/vivianite-jewelry-and-gemstone-information/
• International Gem Society, Phosphophyllite Value, Price, and Jewelry Information: https://www.gemsociety.org/article/phosphophyllite-jewelry-and-gemstone-information/
• Minerals.net, Ametrine: https://www.minerals.net/gemstone/ametrine_gemstone.aspx
• Minerals.net, Cassiterite: https://www.minerals.net/mineral/cassiterite.aspx
• Minerals.net, Vivianite: https://www.minerals.net/mineral/vivianite.aspx
• Geology.com, Cassiterite: https://geology.com/minerals/cassiterite.shtml