THE MINERAL OLIGOCLASE


Oligoclase is not a well-known mineral but has been used as a semi-precious stone under the names of sunstone and moonstone. Sunstone has flashes of reddish color caused by inclusions of hematite. Moonstone shows a glowing shimmer similar to labradorescence, but lacking in color. The display is produced from lamellar intergrowths inside the crystal. These intergrowths result from compatible chemistries at high temperatures becoming incompatible at lower temperatures and thus a separating and layering of these two phases. The resulting shimmer effect is caused by a ray of light entering a layer and being refracted back and forth by deeper layers before it exits the crystal. This refracted ray has a different character than when it went in and produces the moonlike glow. Moonstone is an alternate birthstone for the month of June.

Oligoclase is a member of the Plagioclase Feldspar Group. The plagioclase series comprises minerals that range in chemical composition from pure NaAlSi3 O8, Albite to pure CaAl2 Si2 O8 , anorthite. Oligoclase by definition must contain 90-70% sodium to 10-30% calcium in the sodium/calcium position of the crystal structure. The various plagioclase feldspars are identified from each other by gradations in index of refraction and density in the absence of chemical analysis and/or optical measurements.

All plagioclase feldspars show a type of twinning that is named after albite. Albite Law twinning produces stacks of twin layers that are typically only fractions of millimeters to several millimeters thick. These twinned layers can be seen as striation like grooves on the surface of the crystal and unlike true striations these also appear on the cleavage surfaces. The Carlsbad Law twin produces what appears to be two intergrown crystals growing in opposite directions. Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Although twinned crystals are common, single crystals showing a perfect twin are rare and are often collected by twin fanciers.

PHYSICAL CHARACTERISTICS:

  • Color is usually off-white or gray or pale shades of green, yellow or brown.
  • Luster is vitreous to dull if weathered..
  • Transparency crystals are translucent to transparent.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include blocky, or tabular crystals. Crystals have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is almost universal in all plagioclases. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws. Oligoclase can be found as a major rock forming component in granites and syenites.
  • Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
  • Fracture is conchoidal.
  • Hardness is 6 - 6.5.
  • Specific Gravity is approximately 2.64 - 2.68 (average)
  • Streak is white.
  • Associated Minerals are quartz, muscovite and K-feldspars.
  • Other Characteristics: index of refraction is 1.533 - 1.552. Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations.
  • Notable Occurrences include Sri Lanka; New York, USA; Russia; Sweden and Canada.
  • Best Field Indicators are occurrence, twinning striations, shimmer, density and index of refraction.

Moonstone Jewelry - Hover over an item for more information
Sterling Silver Rainbow Moonstone Stud Earrings
Handmade by Master Artisan. See more details at JeGem.com.Only $96.74 at JeGem.com
no photoSterling Silver Rainbow Moonstone Stud Earrings
$96.74
JeGem.com
DeBuman Sterling Silver Oval Genuine Moonstone Ring DB72R01195S01 Size: 8
Size: 8 DeBuman Sterling Silver Oval Genuine Moonstone Ring This beautiful ring from De Buman features a genuine moonstone in the center. The ring is crafted of sterling silver with a highly polished finish. Features: -Ring.-Metal:Sterling...Only $81.38 at Wayfair
no photoDeBuman Sterling Silver Oval Genuine Moonstone Ring DB72R01195S01 Size: 8
$81.38
Wayfair
Orange, Pink Multi-Stone Ring, Diamonds in 18kt Gold Over Sterling
Smooth cabochons harmonize with sparkling gems on this multi-stone cluster ring. The design features white agate, rose quartz, orange moonstone, and orange opal. Also included are .20 ct. t.w. of white topaz, .50 ct. t.w. of pink tourmaline and diamond...Only $206.25 at Ross-Simons
no photoOrange, Pink Multi-Stone Ring, Diamonds in 18kt Gold Over Sterling
$206.25
Ross-Simons
5.50ct t.w. Green Amethyst, Labradorite Earrings, Moonstone in Silver
A lovely combo of gems that aren't often seen together. 5.50 ct. t.w. of sparkling green amethysts, luminous moonstones and iridescent labradorites compose these creative cluster earrings. Post/clutch, sterling silver earrings.Only $187.50 at Ross-Simons
no photo5.50ct t.w. Green Amethyst, Labradorite Earrings, Moonstone in Silver
$187.50
Ross-Simons
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $83.99 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$83.99
JeGem.com
Sterling Silver Tanzanite, Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $266.99 at JeGem.com
no photoSterling Silver Tanzanite, Rainbow Moonstone Pendant
$266.99
JeGem.com
Sterling Silver Brazilian Amethyst, Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $122.24 at JeGem.com
no photoSterling Silver Brazilian Amethyst, Rainbow Moonstone Pendant
$122.24
JeGem.com
Gray Moonstone and White Topaz Round Drop Earrings in Sterling Silver, One Size
Make a unique statement with these shimmering gray moonstone drop earrings. The round cabochons are accented by sparkling, pave-set white topaz gemstones and suspended from lever-back earwires.Only $89.00 at Blue Nile
no photoGray Moonstone and White Topaz Round Drop Earrings in Sterling Silver, One Size
$89.00
Blue Nile
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $210.74 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$210.74
JeGem.com
Multicolored Moonstone Mosaic Ring, Smoky Quartz, Citrine in Silver
An RS exclusive. Here's a mosaic ring composed of many multi-shaped moonstones in gray, brown, white, and peach, with a .10 carat smoky quartz and a citrine accent. How delightful! Sterling silver ring.Only $129.95 at Ross-Simons
no photoMulticolored Moonstone Mosaic Ring, Smoky Quartz, Citrine in Silver
$129.95
Ross-Simons
Dream 14k Gold Square Rainbow Moonstone Charm Necklace - Lana - Rainbow (14k )
LanaDream 14k Gold Square Rainbow Moonstone Charm NecklaceDetailsLana Dream necklace.14-karat yellow gold.Integrated, square-cut rainbow moonstone pendant.Flat link chain, 18inL.Designer About Lana:Launched in 2002, designer Lana Bramlette's cool,...Only $655.00 at Neiman Marcus
no photoDream 14k Gold Square Rainbow Moonstone Charm Necklace - Lana - Rainbow (14k )
$655.00
Neiman Marcus
Graduated Moonstone Bead Necklace With 14kt Yellow Gold
A dreamy theme is yours with this graduated moonstone bead necklace. Rondelles range from 4x6mm to 7x13mm in size. Necklace features 14kt yellow gold spacers and fastens with 14kt yellow gold fishhook clasp.Only $185.00 at Ross-Simons
no photoGraduated Moonstone Bead Necklace With 14kt Yellow Gold
$185.00
Ross-Simons
Pave-Trim Moonstone-Glass Braided Cord Bracelet, Black - Tai - Black
TaiPave-Trim Moonstone-Glass Braided Cord Bracelet, BlackDetailsTai bracelet features 18-karat yellow gold plated pendant with faceted moonstone glass and pave cubic zirconia.Braided cord bracelet. Beaded ends and small logo charm.Adjustable; 6-8...Only $80.00 at Neiman Marcus
no photoPave-Trim Moonstone-Glass Braided Cord Bracelet, Black - Tai - Black
$80.00
Neiman Marcus
Orange Moonstone, 2.00ct t.w. White Topaz Pendant Necklace Over Sterling. 18"
Soft and serene, this oval orange moonstone of 18 x 12mm catches the eye in an openwork border of 2.00 ct. t.w. white topaz rounds. Suspends from cable chain with lobster clasp. 18kt yellow gold over sterling silver necklace.Only $75.00 at Ross-Simons
no photoOrange Moonstone, 2.00ct t.w. White Topaz Pendant Necklace Over Sterling. 18"
$75.00
Ross-Simons
Sterling Silver Rainbow Moonstone Men's Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $233.24 at JeGem.com
no photoSterling Silver Rainbow Moonstone Men's Pendant
$233.24
JeGem.com
Moonstone Jewelry - Hover over an item for more information
Pave-Trim Moonstone-Glass Braided Cord Bracelet, Black - Tai - Black
TaiPave-Trim Moonstone-Glass Braided Cord Bracelet, BlackDetailsTai bracelet features 18-karat yellow gold plated pendant with faceted moonstone glass and pave cubic zirconia.Braided cord bracelet. Beaded ends and small logo charm.Adjustable; 6-8...Only $80.00 at Neiman Marcus
no photoPave-Trim Moonstone-Glass Braided Cord Bracelet, Black - Tai - Black
$80.00
Neiman Marcus
Golden Maldivian Orbiting Teardrop Earrings - Alexis Bittar - Gold
Alexis BittarGolden Maldivian Orbiting Teardrop EarringsDetailsOrbiting teardrop earrings by Alexis Bittar.Concentric golden drops with porous finish.Silvertone vine with pave Swarovski crystals.Faceted rainbow moonstone drops.4 1/4inL x 1...Only $256.00 at Neiman Marcus
no photoGolden Maldivian Orbiting Teardrop Earrings - Alexis Bittar - Gold
$256.00
Neiman Marcus
Rainbow Moonstone Beaded Bracelet with Diamond Evil Eye - Sydney Evan - Rainbow
Sydney EvanRainbow Moonstone Beaded Bracelet with Diamond Evil EyeDetailsBeaded bracelet by Sydney Evan.Polished rainbow moonstone beads.14-karat yellow gold.Evil Eye charm with enamel, white pave diamonds, and single black diamond.0.13 total white...Only $905.00 at Neiman Marcus
no photoRainbow Moonstone Beaded Bracelet with Diamond Evil Eye - Sydney Evan - Rainbow
$905.00
Neiman Marcus
Mesmerize Moonstone/Onyx Necklace - Lana - Gold
LanaMesmerize Moonstone/Onyx NecklaceDetails14-karat yellow gold.Y-drop with round and marquise-cut rainbow moonstone/black onyx doublets.Figaro chain necklace and pendant trim.Lobster clasp.19 1/2inL.Made in USA.Designer About Lana:Launched in 2002,...Only $940.00 at Neiman Marcus
no photoMesmerize Moonstone/Onyx Necklace - Lana - Gold
$940.00
Neiman Marcus
Moonstone Slice Drop Earrings With Diamonds in 14kt Yellow Gold
So dreamy, the iridescent oval drops of these moonstone slice earrings with .10 ct. t.w. of diamonds reflect the stone s storied history as a mystical gem. Hinged post, 14kt yellow gold earrings.Only $375.00 at Ross-Simons
no photoMoonstone Slice Drop Earrings With Diamonds in 14kt Yellow Gold
$375.00
Ross-Simons
7.70ct t.w. Blue Obsidian, .32ct t.w. Black Diamond Drop Earrings, Moonstones
These blue obsidian and enhanced black diamond drop earrings with moonstones are an innovative array of tonal colors and geometrics. Moonstones link 7.70 ct. t.w. of obsidian stones, framed below with .32 ct. t.w. black diamonds. Post/clutch, sterling...Only $350.00 at Ross-Simons
no photo7.70ct t.w. Blue Obsidian, .32ct t.w. Black Diamond Drop Earrings, Moonstones
$350.00
Ross-Simons
Gray Moonstone and White Topaz Round Drop Earrings in Sterling Silver, One Size
Make a unique statement with these shimmering gray moonstone drop earrings. The round cabochons are accented by sparkling, pave-set white topaz gemstones and suspended from lever-back earwires.Only $89.00 at Blue Nile
no photoGray Moonstone and White Topaz Round Drop Earrings in Sterling Silver, One Size
$89.00
Blue Nile
Round Moonstone Bezel Bracelet in Sterling Silver
This round moonstone bracelet showcases a dreamy stream of glowing bezel-set moonstones all around. Sterling silver bracelet.Only $220.00 at Ross-Simons
no photoRound Moonstone Bezel Bracelet in Sterling Silver
$220.00
Ross-Simons
Sterling Silver Rainbow Moonstone Hook Earrings
Handmade by Master Artisan. See more details at JeGem.com.Only $96.74 at JeGem.com
no photoSterling Silver Rainbow Moonstone Hook Earrings
$96.74
JeGem.com
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $140.99 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$140.99
JeGem.com
Peach Moonstone, Baroque Cultured Pearl Necklace, 14kt Yellow Gold
This moonstone and cultured pearl necklace is a luminous composition of free-form 12-15mm cultured freshwater pearls and peach moonstone beads measuring 10x14mm. Necklace features 14kt yellow gold spacers and fishhook clasp.Only $265.00 at Ross-Simons
no photoPeach Moonstone, Baroque Cultured Pearl Necklace, 14kt Yellow Gold
$265.00
Ross-Simons
Moonstone, .33ct t.w. Diamond Ring in 14kt Yellow Gold Over Sterling
This ring's pear-shaped moonstone is faceted to draw out its pretty shades of blue and bordered by .33 ct. t.w. diamonds. 14kt yellow gold over sterling silver ring.Only $183.75 at Ross-Simons
no photoMoonstone, .33ct t.w. Diamond Ring in 14kt Yellow Gold Over Sterling
$183.75
Ross-Simons
Moonstone-Colored Agate Beaded Bracelet with Pave Gunmetal Bead - Tai - Red
TaiMoonstone-Colored Agate Beaded Bracelet with Pave Gunmetal BeadDetailsThe center bead of this Tai bracelet, encrusted with crystals, delights and dazzles against a string of white moonstone-colored agate beads.Beaded bracelet by Tai.Faceted...Only $110.00 at Neiman Marcus
no photoMoonstone-Colored Agate Beaded Bracelet with Pave Gunmetal Bead - Tai - Red
$110.00
Neiman Marcus
Sterling Silver Rainbow Moonstone Men's Cuff Links
Handmade by Master Artisan. See more details at JeGem.com.Only $209.99 at JeGem.com
no photoSterling Silver Rainbow Moonstone Men's Cuff Links
$209.99
JeGem.com
Orange, Pink Multi-Stone Ring, Diamonds in 18kt Gold Over Sterling
Smooth cabochons harmonize with sparkling gems on this multi-stone cluster ring. The design features white agate, rose quartz, orange moonstone, and orange opal. Also included are .20 ct. t.w. of white topaz, .50 ct. t.w. of pink tourmaline and diamond...Only $206.25 at Ross-Simons
no photoOrange, Pink Multi-Stone Ring, Diamonds in 18kt Gold Over Sterling
$206.25
Ross-Simons
 


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