Oligoclase Gemstone: Properties, Meanings, Value & More

Oligoclase is a gemstone in the feldspar family with popular varieties like sunstone and moonstone. These varieties bring oligoclase optical properties like adularescence and aventurescence.

So, is oligoclase a moonstone? It’d be more accurate to say that moonstone is an oligoclase, though technically moonstone is a mixture of either orthoclase or oligoclase and albite — more on that later.

Is oligoclase rare? Oligoclase minerals are widespread, but gem-quality, transparent oligoclase crystals are rare.

Today, we’ll go over this fascinating feldspar, breaking down oligoclase properties, varieties, prices, and more!

About Oligoclase Stone

Oligoclase is a feldspar mineral with well-known semi-precious gemstone varieties sunstone and moonstone. Other historical terms for oligoclase include:

• Amansite / Amantice / Amantite

• Soda-Spodumene / Sodium Spodumene (both obsolete & inaccurate)

• Adventurine Oligoclase

• Lluvia

• Oligoalbite

• Oligoclasite

• Tschermakite (now a separate stone)

• Sodic plagioclase

Technically, “sodic plagioclase” would be more accurate as a synonym for albite, but it’s also used for sodium-dominant plagioclase feldspars and andesine-feldspar.

As far as birthstones, moonstone is the traditional June birthstone and astrological talisman for Cancer. Sunstone is an astrological birthstone for Libra, as well as an alternate birthstone for July and August.

Oligoclase Uses

As a plagioclase mineral, oligoclase has some major industrial uses. Plagioclase stone uses include:

• Determining rock formation and composition

• Ceramics, glass, and enamel (including false teeth)

• Abrasives

• Filler in rubber, paint, and plastics

• Construction aggregate

Even more interesting: plagioclase is the most plentiful mineral on the crust of Mars!

But how do you identify oligoclase? You have to know its mineral properties first.

Oligoclase Specifications & Characteristics

Oligoclase is part of the feldspar mineral group, which encompasses aluminum tectosilicates containing calcium, sodium, and/or potassium. The most common feldspar subgroups are plagioclase and alkali.

As a calcium or sodium silicate, oligoclase’s formula slightly varies. It may be written as (Ca,Na)(Al,Si)4O8 or (Na,Ca)[Al(Si,Al)Si2O8].

Why the variation? Well, oligoclase feldspar is a member of the plagioclase series, which ranges from albite (sodium feldspar; NaAlSi3O8) to anorthite (calcium feldspar; CaAl2Si2O8).

In the series, oligoclase’s composition is closer to albite, at 10 to 30 percent anorthite and 70 to 90 percent albite. Other minerals in the series, in ascending order getting closer to anorthite, are andesine, labradorite, and bytownite.

One subdivision of oligoclase sometimes called “oligoclase-albite” has 20 to 80 percent anorthite and 10 to 90 percent albite.

Does oligoclase have twinning? Often, yes. Many tabular oligoclase crystals exhibit Albite, Carlsbad, or Pericline twinning. Oligoclase twinning is characteristic of many plagioclase feldspars.

Oligoclase properties listed:

• Mohs hardness: 6-6.5

• Color: Colorless, white, pale yellow, orange, green, blue, red, brown, gray

• Crystal structure: Triclinic

• Luster: Vitreous

• Transparency: Transparent to opaque

• Refractive index: 1.533-1.552

• Density: 2.62-2.67

• Cleavage: Perfect on {001}, Good on {010}, Poor on {110}

• Fracture: Irregular/uneven, splintery, conchoidal, or subconchoidal

• Streak: White

• Luminescence: Fluorescence rarely present - faint red to faint white in SW-UV

• Pleochroism: Usually none; Occasionally present - colorless to greenish-blue or shades of yellow

• Birefringence: 0.007-0.011

• Dispersion: Weak to none

• Optical phenomena: Adularescence, sometimes chatoyancy (moonstone); Aventurescence, sometimes asterism and adularescence (sunstone)

Types of Oligoclase

The main oligoclase gemstones are sunstone and moonstone, which we’ll break down next. Other mineral varieties include:

• Lazur-Feldspath: Blue feldspar occurring with lapis lazuli near Lake Baikal, Russia

• Peristerite: Feldspar mixture, primarily albite or oligoclase, often displaying iridescence

Onto the show-stoppers!

Sunstone

Sunstone is a commonly reddish-orange gemstone known for its aventurescence (or schiller), a metallic glittering effect caused by tiny reflective platelets of hematite or goethite. Not all sunstones have this effect, though, so many gemologists call sunstones with schiller “aventurine (or aventurescent) feldspar.”

Additionally, not all sunstones fall under the same feldspar family. There are three types:

1. Orthoclase Sunstone

2. Oligoclase Sunstone

3. Labradorite Sunstone

Oligoclase and labradorite sunstones have slightly higher densities, refractive indices, and birefringence values than orthoclase sunstone.

Oregon sunstones (or “lehrite”) are labradorite sunstones that get their schiller from copper inclusions. Rainbow lattice sunstones are orthoclase types with a unique iridescent lattice pattern.

The term “sunstone” may sometimes be a misnomer though. Sometimes sellers use it for simulants made of man-made glass, more accurately called “goldstone” or “aventurine glass.” The so-called “Viking sunstone” was likely calcite or iolite.

Moonstone

Moonstone is a feldspar variety known for its internal moonlight-like glow called “adularescence.” Some gemologists consider moonstone an orthoclase variety with alternating layers of orthoclase and albite. Others classify different feldspars like oligoclase-peristerite mixtures as moonstone.

Regardless, moonstone is most valuable when colorless with a blue glow. It can also be shades of orange, gray, green, yellow, brown, and even black.

Some moonstone misnomers include:

• Rainbow Moonstone: Labradorite variety with adularescence

• Blue Moonstone: Sometimes used for chalcedony treated to be blue

• Ceylon Opal: Opal-like moonstone from Sri Lanka

Man-made opalite may be erroneously labeled “moonstone.”

Perthite

Perthite is a mixture of two different feldspars in one rock, usually albite and/or oligoclase with microcline or orthoclase. The various types can be categorized by the size of the intergrowth — cryptoperthite, microperthite, and macroperthite — or which feldspar minerals formed first — antiperthite and mesoperthite.

There are also different types according to the feldspars present:

• Perthite: Usually microcline with albite or oligoclase

• Amazonite Perthite: Albite or oligoclase and amazonite (green microcline)

• Orthoclase Perthite: Albite or oligoclase and orthoclase

The stone is often white or brown, sometimes with white or gold iridescence.

Oligoclase History

Swedish chemist Jacob Berzelius (or Baron Jöns Jacob Berzelius, officially) first recognized oligoclase as a distinct species in 1824 based on specimens found in Stockholm, Sweden. Berzelius named it Natron-spodumen, or “soda-spodumene” because it resembled spodumene.

In 1826, German mineralogist August Breithaupt chose the name “oligoclase.” The name derives from the Ancient Greek terms oligos, meaning “little,” and klân, meaning “to break,” because the cleavage was less perfect (further from a 90° angle) than that of albite.

Funny enough, Jacob Berzelius also chose the name “albite” with Johan Gottlieb Gahn in 1815.

Spiritually, what are the benefits of oligoclase?

Oligoclase Healing Properties

As a primarily white healing stone, oligoclase offers the cleansing and protective properties of white gemstones. It’s also a powerful crown chakra stone.

Physical Healing

Physically, oligoclase is said to treat:

• Arthritis

• Hair loss

• Muscle atrophy

• Skin disorders

• Insomnia

Emotional Healing

Emotionally, oligoclase may provide relief from feelings of stress, anxiety, or despair. The crystal is believed to boost mental clarity, concentration, and joy.

Oligoclase Gemstone Properties

Oligoclase gemstone value depends on color, cut, clarity, transparency, and carat weight. (For sunstone and moonstone grading, check out their respective info guides!)

Color

Oligoclase is typically white, colorless, or light yellow. It can also be gray, green, red, blue, orange, or brown.

Brighter colors can be more valuable, especially when colorful effects like iridescence or adularescence are present.

Cut

Facetable oligoclase is pretty rare, making faceted gems more valuable. Stones with chatoyancy must be cut as cabochons. Many adularescent stones are also cut as cabochons.

Clarity & Transparency

In most oligoclase gems, visible inclusions reduce value. The exceptions are inclusions that produce aventurescence or asterism (seen in some sunstones).

Since transparent oligoclase crystals are rare, they’re more valuable.

Carat Weight

Most oligoclase gemstones are under 2-3 carats, but size can vary by source. For instance, oligoclase gems from North Carolina and Canada have been up to around 5 carats. The largest oligoclase crystals are found in Arendal, Norway.

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

Oligoclase Formation & Sources

What type of rock is oligoclase found in? A lot! Most often, it forms in igneous rocks like diorite, syenite, and granite.

It can also form in lava rocks like trachyte and andesite or medium- to high-grade metamorphic rocks like gneiss.

Oligoclase often forms near orthoclase or biotite.

Mining Locations

Where is oligoclase found? Oligoclase minerals are found all over the world, but facetable material comes from:

• North Carolina, USA

• Norway

• Canada

• Connecticut, USA

• Kenya

• India

Oligoclase Price & Value

Faceted oligoclase gemstones tend to be priciest, given their rarity.

Generally, faceted oligoclase gems of varying quality can be around $20 to $100 per carat or higher. High-quality faceted oligoclase gems are around $55 to $110 per carat.

Cat’s eye oligoclase moonstone cabochons vary in cost at about $10 to $650, or about $6 to $15 per carat.

For specific prices of moonstone and sunstone, check out their individual info guides.

Oligoclase Care and Maintenance

Though oligoclase hardness is relatively high, its perfect cleavage and brittle toughness mean gentle gemstone care is key. We recommend protective settings for most oligoclase jewelry, particularly rings.

Clean oligoclase with warm water, mild soap, and a soft toothbrush. Avoid mechanical systems (e.g. ultrasonic or steam cleaners).

Store separately from other gems to avoid scratches.

From Sunshine to Moonlight, Oligoclase is Perfect for Any Day!

Oligoclase is a beautiful gem on its own, but its varieties take the diversity up a notch. From the warm sparkling hues of sunstone to the soothing blue glow of moonstone, there’s an oligoclase gem for any taste or time of day!

Buy oligoclase gemstones today!