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
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
KALAN by Suzanne Kalan Stone & Sapphire Pendant Necklace
A highly faceted bezel-set semiprecious stone offers a gorgeous pop of color in a feminine gold necklace further illuminated by sparkling pave sapphires. Color(s): rose gold/ amethyst, rose gold/ white moonstone, white gold/ sky blue topaz, yellow...Only $760.00 at Nordstrom
no photoKALAN by Suzanne Kalan Stone & Sapphire Pendant Necklace
$760.00
Nordstrom
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
Gray Moonstone and 1.65 ct. t.w. Diamond Earrings in Sterling Silver
Flickering with faceted moonstones in a moody shade of gray, these elegant drop earrings are silhouetted by 1.65 ct. t.w. diamonds. Leverbacks, sterling silver earrings with a black rhodium finish.Only $750.00 at Ross-Simons
no photoGray Moonstone and 1.65 ct. t.w. Diamond Earrings in Sterling Silver
$750.00
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
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 Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $98.24 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$98.24
JeGem.com
Moonstone Mosaic Necklace in 14kt Yellow Gold. 18"
An RS exclusive. This gorgeous moonstone mosaic necklace features dreamy moonstones artfully arranged in oval, round and pear-shaped bezels. 14kt yellow gold necklace.Only $285.00 at Ross-Simons
no photoMoonstone Mosaic Necklace in 14kt Yellow Gold. 18"
$285.00
Ross-Simons
Moonstone and .10 ct. t.w. Diamond Drop Earrings in Sterling Silver
These faceted moonstone and .10 ct. t.w. diamond earrings have an ethereal presence. Luminous pear-shaped moonstone drops are topped with clusters of diamond rounds in a dreamy display. Leverback, sterling silver earrings.Only $135.00 at Ross-Simons
no photoMoonstone and .10 ct. t.w. Diamond Drop Earrings in Sterling Silver
$135.00
Ross-Simons
Sterling Silver Rainbow Moonstone Leverback Earrings
Handmade by Master Artisan. See more details at JeGem.com.Only $77.99 at JeGem.com
no photoSterling Silver Rainbow Moonstone Leverback Earrings
$77.99
JeGem.com
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
Moonstone and .15 ct. t.w. CZ Drop Earrings in 14kt Gold Over Sterling
Bring an element of mystique to your wardrobe with this pair of drop earrings. Round moonstone cabochons, aswirl with subtle colors, are held in beautifully textured frames. .15 ct. t.w. of round brilliant-cut CZs trim the leverbacks. 14kt yellow gold...Only $112.50 at Ross-Simons
no photoMoonstone and .15 ct. t.w. CZ Drop Earrings in 14kt Gold Over Sterling
$112.50
Ross-Simons
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $125.24 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$125.24
JeGem.com
Multi-Stone Bead Necklace in 14kt Gold Over Sterling
A feast for the eyes! This multi-stone bead and cultured baroque pearl necklace features amethyst, lapis, carnelian, chalcedony, turquoise, hematite, tiger s eye, agate, pink coral and moonstone and a gray baroque cultured freshwater pearl. Springring...Only $195.00 at Ross-Simons
no photoMulti-Stone Bead Necklace in 14kt Gold Over Sterling
$195.00
Ross-Simons
Moon White-Facet Pinch Bracelet - Tai - Moon
TaiMoon White-Facet Pinch BraceletDetails18-karat white gold-plated open bracelet.End caps feature faceted moonstone-colored glass and pave cubic zirconia.Slightly malleable; opening for slip-on style.6in round.Disk, 10mm (approx. 2/5in).6in...Only $105.00 at Neiman Marcus
no photoMoon White-Facet Pinch Bracelet - Tai - Moon
$105.00
Neiman Marcus
Moonstone Jewelry - Hover over an item for more information
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $161.99 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$161.99
JeGem.com
Sterling Silver Rainbow Moonstone Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $143.24 at JeGem.com
no photoSterling Silver Rainbow Moonstone Pendant
$143.24
JeGem.com
Rainbow Moonstone Beaded Bracelet with Diamond Hamsa - Sydney Evan - Rainbow
Sydney EvanRainbow Moonstone Beaded Bracelet with Diamond HamsaDetailsBeaded bracelet by Sydney Evan.Polished rainbow moonstone beads, 10mm.14-karat yellow gold.Medium Hamsa charm with white pave diamonds and turquoise cabochon.0.23 total diamond carat...Only $950.00 at Neiman Marcus
no photoRainbow Moonstone Beaded Bracelet with Diamond Hamsa - Sydney Evan - Rainbow
$950.00
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
Gray Moonstone and White Topaz Round Ring in Sterling Silver, One Size
Make a unique statement with this shimmering gray moonstone ring. The round cabochon is accented by a halo of sparkling, pave-set white topaz gemstones.Only $129.00 at Blue Nile
no photoGray Moonstone and White Topaz Round Ring in Sterling Silver, One Size
$129.00
Blue Nile
Mesmerize Moonstone/Onyx Earrings - Lana - Gold
LanaMesmerize Moonstone/Onyx EarringsDetailsLana juxtaposes bold gold and misty moonstone to create these mysterious, mesmerizing earrings. 14-karat yellow gold.Rainbow moonstone and black onyx doublet drops.Figaro chain trim.French wire...Only $775.00 at Neiman Marcus
no photoMesmerize Moonstone/Onyx Earrings - Lana - Gold
$775.00
Neiman Marcus
Rainbow Moonstone Triple Drop Earrings in 18kt Gold Over Sterling
These rainbow moonstone drop earrings are so elegant! Pear-shaped and round rainbow moonstones lend their luminous presence to lovely drops. Earwire, 18kt yellow gold over sterling silver earrings.Only $85.00 at Ross-Simons
no photoRainbow Moonstone Triple Drop Earrings in 18kt Gold Over Sterling
$85.00
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
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
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
Moonstone Mosaic Necklace in 14kt Yellow Gold. 18"
An RS exclusive. This gorgeous moonstone mosaic necklace features dreamy moonstones artfully arranged in oval, round and pear-shaped bezels. 14kt yellow gold necklace.Only $285.00 at Ross-Simons
no photoMoonstone Mosaic Necklace in 14kt Yellow Gold. 18"
$285.00
Ross-Simons
Rainbow Moonstone Spellbound Gypsy Necklace - Lana - Rainbow
LanaRainbow Moonstone Spellbound Gypsy NecklaceDetails14-karat yellow gold.Flat link necklace.Links wrap around marquise-cut rainbow moonstone charms.22inL.Lobster clasp.Designer About Lana:Launched in 2002, designer Lana Bramlette's cool, minimalist...Only $890.00 at Neiman Marcus
no photoRainbow Moonstone Spellbound Gypsy Necklace - Lana - Rainbow
$890.00
Neiman Marcus
.50ct t.w. Multi-Stone, Mixed Cabochon Cluster Ring Over Sterling
This ring has the look of a handcrafted artisanal piece, with a cluster of cabochons and multi-stones set on a openwork band. Showcases moonstone, blue agate and rose quartz with .50 ct. tot. gem wt. of pear-shaped peridot, blue topaz and amethyst....Only $221.25 at Ross-Simons
no photo.50ct t.w. Multi-Stone, Mixed Cabochon Cluster Ring Over Sterling
$221.25
Ross-Simons
Opaque Multi-Stone Drop Necklace in Sterling Silver. 18"
A unconventional work of wearable art. The etched centerpiece of this necklace presents opaque cabochons of labradorite, moonstone, garnet and amethyst. On a wheat chain with a lobster clasp. Sterling silver necklace.Only $146.25 at Ross-Simons
no photoOpaque Multi-Stone Drop Necklace in Sterling Silver. 18"
$146.25
Ross-Simons
Moonstone and .26 ct. t.w. Diamond Ring in Sterling Silver
Like something of a dream, four iridescent rainbow moonstone squares shimmer on this stacked-look ring. Set with a black rhodium-finish and .26 ct. t.w. diamonds. Sterling silver ring.Only $245.00 at Ross-Simons
no photoMoonstone and .26 ct. t.w. Diamond Ring in Sterling Silver
$245.00
Ross-Simons
 


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