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Sanidine Gemstone: Properties, Meanings, Value & More

サニディン宝石：特性、意味、価値など

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Sanidine is a transparent to translucent feldspar gemstone that’s usually colorless or white but can be yellow or brown. The stone is related to the gemstones amazonite and orthoclase.

Is sanidine a rare mineral? Yep, the mineral is fairly rare and gemstone material is extremely rare. This may be surprising considering feldspars are the most abundant minerals on Earth and make up around 60 percent of the crust (Earth’s surface).

Ready to learn more about the rare feldspar sanidine? We’ll fill you in on sanidine properties, prices, benefits, and history.

Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

About Sanidine Stone

Sanidine can be used as a semi-precious gemstone, with other monikers including:

• Glassy feldspar

• Rhyacolite / Riacolite

• Gränzerite

It’s easy to mistake sanidine for orthoclase. But what’s the difference between sanidine and orthoclase?

They’re both very similar feldspar minerals, but they can be distinguished by their formation, optic angles (2V), and transparency.

1. Formation: Sanidine forms at high temperatures and orthoclase forms at lower medium temperatures, forming more ordered crystals compared to sanidine’s disordered crystals.

2. Optic Angle: A thin section of sanidine and orthoclase will reveal that orthoclase has a higher optic angle (2V of 65-75) than sanidine (2V of 18-63).

3. Transparency: Both are commonly colorless to white, but orthoclase is often cloudy while sanidine is often clear.

Note: You may need to see sanidine under a microscope to make these distinctions.

Sanidine Uses

Although sanidine is too rare to have many industrial applications, it can be used for radiometric dating. Radiometric dating involves analyzing radioactive isotopes in materials like rocks or carbon to determine how old they are.

In the western US, sanidine phenocrysts (big, noticeable crystals) present in rhyolite ash beds are helpful in dating the ash beds. This particular type of radiometric dating is the K-Ar dating method or potassium-argon dating, which measures the ratio of radioactive potassium to radioactive argon.

But how do you identify sanidine? First, you’ll need to get familiar with its mineral properties.

Pictured above: Twinned sanidine crystals (combination of Carlsbad and Baveno twins)

Sanidine Specifications & Characteristics

The sanidine formula may be written as K(AlSi3O8) or (K,Na) (AlSi3O8), as the stone typically contains around 30 percent (but potentially up to 62 percent) sodium. Common impurities are iron, calcium, sodium, and water.

The feldspar group consists of aluminum tectosilicates with two major groupings: plagioclase (sodium-calcium) and alkali (potassium-sodium).

Sanidine falls under the alkali group, specifically the larger K-feldspar alkali subgroup alongside orthoclase and microcline.

The three minerals are polymorphous (same composition, different crystal structure). Microline is triclinic while sanidine and orthoclase are monoclinic. Sanidine is sometimes considered a variety of orthoclase.

At high temperatures, sanidine forms a series with high albite (or “analbite”).

Petrologists classify 10- to 36-percent K-feldspar intermediates in this series as anorthoclase and 36- to 100-percent K-feldspars in the series as sanidine. However, other scientists have stopped using the term “anorthoclase,” opting for “albite” if sodium is greater than potassium and “sanidine” if potassium is greater than sodium.

Sanidine Crystal Habits

Sanidine crystals can be tabular, acicular (needle-like), or prismatic. Most crystals are flattened with prisms that can be lamellar (tightly packed layers) or elongated and parallelepipedal (parallelogram faces).

Like most feldspars, sanidine crystals commonly exhibit twinning.

The most common type for sanidine is Carlsbad (or Karlsbad), a form of penetration twinning where two intergrown crystals look like they’re growing in opposite directions.

Two rarer types are Baveno and Manebach twinning. The Baveno type is a form of contact twinning on the {021} plane, while Manebach twinning occurs on the {001} plane. The result in both cases is a set of crystals with notches and one notable mirror plane (or “symmetry plane”).

Perfect twinned sanidine crystals are rare and sought-after by some collectors.

Here are all of sanidine’s properties listed:

• Mohs hardness: 6-6.5

• Color: Colorless, white, yellow, brown

• Crystal structure: Monoclinic

• Luster: Vitreous (glassy); Pearly on cleavage

• Transparency: Transparent to translucent

• Refractive index: 1.516-1.531

• Density: 2.52-2.62

• Cleavage: Perfect on {001}, Distinct/good on {010}

• Fracture: Uneven/irregular, conchoidal, or splintery; Parting common on {100}

• Streak: White

• Luminescence: Sometimes fluorescence (usually Madagascar specimens) - weak red-orange in LW-UV & SW-UV

• Pleochroism: Weak to unobservable

• Birefringence: 0.003-0.007

• Dispersion: 0.012 (weak)

• Optical phenomenon: Adularescence (rare)

Pictured above: Azulicite crystal | Image credit: Didier Descouens, CC-BY-SA-4.0

Types of Sanidine

Sanidine has two mineral forms, two subtypes based on impurities, and two gemstone varieties.

The two sanidine mineral forms are:

• High Sanidine: High-temperature form; Probably stable above 800°C

• Low Sanidine: Low-temperature form; Probably stable between 650°C and 800°C

Subtypes based on impurities are:

• Barium-Sanidine: Contains 5 percent barium oxide (BaO)

• Ferrisanidine: Iron analogue with the formula K(Fe3+Si3O8)

Lastly, the gemstone varieties are:

• Azulicite: Blue, transparent, and iridescent variety

• Citron Feldspar: Trade name for yellow, gem-quality specimens like those from Madagascar

Some gemologists consider adularescent sanidine stones a type of moonstone, though most classify moonstone under orthoclase or oligoclase.

Additionally, sanidine is often visibly present in the rhyolite rocks comendite (beside quartz and albite) and pantellerite.

Spiritually, what is the meaning of the crystal sanidine?

Sanidine Meaning & History

As a feldspar gem, sanidine inherently symbolizes creativity, self-awareness, and manifestation.

Individually, sanidine represents resilience, self-acceptance, and light.

The name “sanidine” derives from the Greek terms sanis, meaning “little plate” or “tablet,” and idos, meaning “to see” or “to appear.” German mineralogist Karl Wilhelm Nose chose the name in 1808, alluding to sanidine’s often flattened, tabular crystals.

Sanidine’s type locality is the legendary Drachenfels hill in Germany. It’s legendary for the many dragon-related legends surrounding the area — after all, Drachenfels is German for “Dragon’s Rock.”

German chemist Martin Heinrich Klaproth published some of the earliest analyses of sanidine specimens from this area in 1810.

Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Sanidine Healing Properties

As a primarily colorless healing stone, sanidine offers the cleansing and purifying properties of colorless gems. Yellow sanidine can be used as a solar plexus chakra stone.

Physical Healing

Physically, sanidine is believed to help treat issues related to:

• Menstrual pain

• Circulation

• Nervous system

• Infections

• Skin issues like irritation or rashes

Emotional Healing

Emotionally, sanidine is believed to alleviate feelings of grief, anxiety, and frustration. Crystal healers recommend it for those struggling to open up about their emotions or anyone wanting to be calmer and more confident.

Pictured above: Faceted azulicite (sanidine variety) gemstone | Image credit: Didier Descouens, CC-BY-SA-4.0

Sanidine Gemstone Properties

Besides their extreme rarity, sanidine gemstone value depends on color, cut, clarity, transparency, and carat weight. There are no known treatments or synthetic sanidine gemstones.

Color

The most common sanidine color is white to colorless, so yellow hues may be more desirable, but not always. Germany, Mexico, and Madagascar have produced colorless, yellow, and light brown sanidine gems.

Cut

Sanidine crystals are rarely found in large enough sizes to facet, so faceted options are quite rare and valuable. Some specimens may be cut into cabochons, beads, or sold rough (uncut).

Clarity & Transparency

Clarity, the degree of visible inclusions, can affect sanidine’s transparency. Higher transparency means higher value.

Sanidine has occasionally been found as an inclusion in precious gems like sapphire and diamond.

Inclusions inside sanidine phenocrysts and megacrystals ejected from volcanoes have also helped scientists understand what was happening inside the volcanoes before and during they erupted. These inclusions included barium, glass, and fluid phase bubbles.

Carat Weight

Gem-quality, sizable sanidine crystals are rare. Most larger gem specimens come from Madagascar and Germany. One exceptional faceted gem from Germany (part of the Eduard Gübelin Collection) was nearly 30 carats!

Sanidine Formation & Sources

Sanidine crystallizes from high-temperature, rapidly cooled lava. If the lava cools slowly, orthoclase forms. While low and high sanidine forms at temperatures above 650°C, temperatures below that lead to orthoclase and microcline. Sanidine can also gradually recrystallize into orthoclase over long geological periods.

What kind of rock is sanidine found in? It’s found in volcanic discharges or acidic volcanic rocks like rhyolite, dacite, lamproite, buchites, obsidian, and trachyte.

Mining Locations

Sanidine gem material comes from:

• Germany

• Madagascar

• Myanmar

• Sri Lanka

• USA (California, Colorado, Idaho, Oregon)

How much does sanidine cost?

Sanidine Price & Value

Faceted sanidine gemstones online can range from $10 to $215 per carat, but many of these are likely mislabeled orthoclase or other feldspar varieties.

You can find sanidine cabochons for around $10 per carat or about $50 each.

Raw crystal specimens are most affordable, often available for under $1 per carat.

Pictured above: Pseudobrookite needle in tabular sanidine crystals | Image credit: Fred Kruijen, CC-BY-SA-3.0

Sanidine Care and Maintenance

Before we wrap up, let’s discuss gemstone care.

Unfortunately, you probably won’t find much sanidine jewelry available. Besides its rarity, sanidine has poor wearability. That said, if you do find jewelry, be sure to get protective settings and only wear it occasionally.

Sanidine is soluble in hydrofluoric acid and brittle, so handle it gently. Only clean it with warm water, mild soap, and a soft toothbrush.

Stand Out with Sanidine!

Despite the abundance of feldspar minerals, sanidine is an unusual member of the pack that shines for its rarity and cooling clear to warm yellow hues — and adding this gem to your collection can help you stand out from the pack, too.

Buy sanidine and other rare gemstones today!