Moonstone (gemstone)

Last updated
Category Orthoclase variety
(repeating unit)
Crystal system Monoclinic
ColorCan be numerous colors, including blue, grey, white, pink, peach, green and brown, as well as colorless
Cleavage perfect
Fracture uneven to conchoidal
Mohs scale hardness6.0
Luster Opalescent
Streak white
Specific gravity 2.54–2.66
Optical propertiesfor orthoclase and sanidine, biaxial (–); for oligoclase, biaxial +/–
Refractive index 1.518–1.547
Birefringence 0.005–0.01
Dispersion 0.012
A small rough moonstone sample Raw Moonstone.jpg
A small rough moonstone sample

Moonstone is a sodium potassium aluminium silicate ((Na,K)AlSi3O8) of the feldspar group that displays a pearly and opalescent schiller. [1] [2] An alternative name for moonstone is hecatolite [2] (from goddess Hecate).



The name moonstone derives from the stone's characteristic visual effect, called adularescence (or schiller), which produces a milky, bluish interior light. This effect is caused by light diffraction through alternating layers of orthoclase and albite within the stone. The diffracted light varies from white to blue, depending on the thinness of the albite layers. [1] More technically, this micro-structure consists of regular exsolution layers (lamellae) of different alkali feldspars (orthoclase and sodium-rich plagioclase).

Polished moonstones often display chatoyancy ("cat's eye" effect), where a luminous streak appears through the stone. Asterism is rare and produces four-legged stars. [1]


Moonstone cabochon Moonston.jpg
Moonstone cabochon

The most common moonstone is of the orthoclase feldspar mineral adularia, named for an early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard. [1] [ better source needed ] A solid solution of the plagioclase feldspar oligoclase +/− the potassium feldspar orthoclase also produces moonstone specimens.

Deposits of moonstone occur in Armenia (mainly from Lake Sevan), Australia, the Austrian Alps, Mexico, Madagascar, Myanmar, Norway, Poland, India, Sri Lanka, and the United States. [2] [3] Historically, the most valuable, transparent moonstones with strong blue sheen came from Myanmar. [1] Today, most commercial moonstones come from Sri Lanka. [3]

In culture

Moonstone has been used in jewellery for millennia, including ancient civilizations. The Romans admired moonstone, as they believed it was derived from solidified rays of the Moon. [4] Both the Romans and Greeks associated moonstone with their lunar deities. In more recent history, moonstone became popular during the Art Nouveau period; French goldsmith René Lalique and many others created a large quantity of jewellery using this stone. [5]

The moonstone is the Florida State Gemstone; it was designated as such in 1970 to commemorate the Moon landings, which took off from Kennedy Space Center. However, it does not naturally occur in the state. [6]

Related Research Articles

<span class="mw-page-title-main">Amazonite</span> Green silicate mineral

Amazonite, also known as amazonstone, is a green tectosilicate mineral, a variety of the potassium feldspar called microcline. Its chemical formula is KAlSi3O8, which is polymorphic to orthoclase.

In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava, and have low temperatures to keep the felsic minerals molten.

<span class="mw-page-title-main">Feldspar</span> Group of rock-forming minerals

Feldspar is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.

<span class="mw-page-title-main">Orthoclase</span> Tectosilicate mineral found in igneous rock

Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture", because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar. The gem known as moonstone (see below) is largely composed of orthoclase.

<span class="mw-page-title-main">Microcline</span> Igneous rock-forming tectosilicate mineral

Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures than orthoclase. Sanidine is a polymorph of alkali feldspar stable at yet higher temperature. Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline.

<span class="mw-page-title-main">Plagioclase</span> Type of feldspar

Plagioclase ( PLAJ-(ee)-ə-klayss, PLAYJ-, -⁠klayz) is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or "record-groove" effect.

<span class="mw-page-title-main">Aventurescence</span> Optical reflectance effect seen in certain gems

In gemology, aventurescence is an optical reflectance effect seen in certain gems. The effect amounts to a metallic glitter, arising from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour. In aventurine quartz chrome-bearing fuchsite produces a green stone, and various iron oxides produce a red stone.

Moonstone may refer to:

<span class="mw-page-title-main">Albite</span> Mineral, Na-feldspar, Na-silicate, tectosilicate

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi
. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. It is a common constituent in felsic rocks.

<span class="mw-page-title-main">Asterism (gemology)</span>

An asterism is a star-shaped concentration of light reflected or refracted from a gemstone. It can appear when a suitable stone is cut en cabochon.

<span class="mw-page-title-main">Perthite</span> Intergrowth of two feldspars

Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). Typically, the host grain is orthoclase or microcline, and the lamellae are albite. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in roughly equal proportions the result is a mesoperthite.

<span class="mw-page-title-main">Oligoclase</span> Sodium-rich plagioclase feldspar mineral

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). The albite:anorthite molar ratio of oligoclase ranges from 90:10 to 70:30.

<span class="mw-page-title-main">Essexite</span> Igneous rock type

Essexite, also called nepheline monzogabbro, is a dark gray or black holocrystalline plutonic igneous rock. Its name is derived from the type locality in Essex County, Massachusetts, in the United States.

<span class="mw-page-title-main">Sanidine</span> Form of potassium feldspar

Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable.

<span class="mw-page-title-main">Sunstone</span> Brown-orange feldspar

Sunstone is a microcline or oligoclase feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern Norway, Sweden, various United States localities and on some beaches along the midcoast of South Australia.

Saussurite is a mineral aggregate which is formed as a hydrothermal alteration product of plagioclase feldspar. It appears very similar to zoisite with a green or grayish-green color, it has been used as a substitute or simulant for jade.

<span class="mw-page-title-main">Myrmekite</span> Tiny intergrowths of quartz and feldspar in rocks

Myrmekite is a vermicular, or wormy, intergrowth of quartz in plagioclase. The intergrowths are microscopic in scale, typically with maximum dimensions less than 1 millimeter. The plagioclase is sodium-rich, usually albite or oligoclase. These quartz-plagioclase intergrowths are associated with and commonly in contact with potassium feldspar. Myrmekite is formed under metasomatic conditions, usually in conjunction with tectonic deformations. It has to be clearly separated from micrographic and granophyric intergrowths, which are magmatic.

<span class="mw-page-title-main">Adularescence</span> Milky luster or iridescence originating from below the surface of gemstones

Adularescence is an optical phenomenon that is produced in gemstones like moonstone. The optical effect is similar to labradorescence and aventurescence.

<span class="mw-page-title-main">Rainbow lattice sunstone</span> Australian feldspar with geometric inclusions

Rainbow lattice sunstone, also known as rainbow lattice, is a type of orthoclase feldspar that exhibits a rare combination of aventurescence, adularescence, and a distinctive iridescence lattice pattern. The iridescence lattice pattern consists of inclusions that are the result of crystallographically oriented exsolution crystals within the feldspar crystal. Sunstone refers to its physical appearance instead of its chemical composition.


  1. 1 2 3 4 5 Moonstone Gemological Information International Gem Society, Retrieved 01-05-15
  2. 1 2 3 Moonstone, , retrieved 2022-02-06
  3. 1 2 "Moonstone" Encyclopædia Britannica, 2011. Web. 20 Jan. 2011.
  4. "Moonstone" American Gem Trade Association. Retrieved 21 January 2011.
  5. "Moonstone" International Colored Gemstone Association. Retrieved 26 April 2012.
  6. "Moonstone – Florida State Symbols". Florida Division of Historical Resource. Retrieved 1 Sep 2011.