Gems | Moonstone | Feldspar | Adularia | Sanidine

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This week I am continuing the exploration of Gems in the Feldspar family. Last week I introduced you to the sub-groups in this family and, in particular, the “Alkali” subgroup. I told you about its’ most famous member, Moonstone. I find it interesting, that while investigating Moonstone, I have found many conflicting statements as to which form(s) of Feldspar are included. At this point, I have determined the soft pastel Moonstones to be Adularia and Sanidine, and the “Rainbow Moonstone” to be Oligoclase (“Plagioclase” subgroup). This week we’ll explore the rest of the gems in the “Alkali” sub-group.
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As a reminder, lets’ review these two Feldspar sub-groups.

The Sodium Potassium “Alkali” Feldspar – (Sodium/Potassium Aluminum
Silicates).
Orthoclase
Sanidine (Moonstone)
Adularia (Moonstone)
Microcline (Amazonite)

The Sodium Calcium “Plagioclase” Feldspar – (Sodium/Calcium Aluminum
Silicates).
Oligoclase (Rainbow Moonstone)
Sunstone
Peristerite – (Labradorite)
Bytownite
Andesine
Anorthite

Between the two sub-groups is Albite – (Sodium Aluminum Silicate).
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The next important gem in the Sodium Potassium “Alkali” Feldspar sub-group is Microcline. Amazonite is a form of Microcline Feldspar.

Although Microcline Feldspar is found in the following colors; colorless, white, yellowish, pinkish, and green, only the light to dark green variety is considered to be Amazonite. There seem to be two varieties of Amazonite. In one, the color is a mottled soft blue-green to pale blue. The other, “Russian Amazonite” (also found in other parts of the world), is a deeper green and can have green or white striations.

The stories behind the name Amazonite vary. Some references claim the name is ancient and the gem was supposedly connected with the ancient female warriors (Amazons) of Mediterranean mythologies. Other references claim the gem was named for the Amazon River, a place where Amazonite was found. I could not find a definitive answer.

Historically, the deep green “Russian” Amazonite has been used, throughout the Middle East and Asia Minor, as beads and amulets and for décor, for thousands of years. I’ve seen beautiful green Amazonite antiquities and beads from ancient Egypt and Asia Minor that are over 5,000 years old. Currently, in Morocco and North Africa, this same deep green gemstone (can be striated) is called “Green Stone”, and it is cherished in the same way that Turquoise is cherished by the American Indians.

The soft green-blue form of Amazonite is said to be a “soothing stone”, and believe it or not, it is, also, claimed to wake up lazy teenagers and give them energy. The deeper green “Russian Amazonite” is said to be a “stone of courage”.

Amazonite is found in Colorado (USA), Russia, Brazil, East Africa, Madagascar, etc.

Another gem Feldspar in this subgroup is Orthoclase. Although Adularia (Moonstone) is a form of Orthoclase, when this champaign-colored Feldspar gem is clear (rare), it is faceted and used in jewelry or held in rare gem collections.

Orthoclase is found in: Twentynine Palms, CA (USA) [“well formed crystals & twin crystals up to 200mm across”]; Elba, Italy; Czech Republic; Poland; Itrongay, Madagascar [“Yellow gemmy crystals up to 70mm across”]; Black Hills, South Dakota (USA) [“Gigantic crystals up to tens of meters long”]; Germany; Switzerland; Sri Lanka.

The last gem in this subgroup is smokey-brown Sanidine. Like Orthoclase, opaque gem Sanidine can be found as a Moonstone, and when clear, this gem is faceted for jewelry and rare gem collections.

Sanindine is found in: Germany [“Well formed crystals…up to 400mm in size”]; France; British Columbia, Canada; Bulgaria.
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Next week we will explore the Sodium Calcium “Plagioclase” Feldspar subgroup. The Plagioclase subgroup includes: “Rainbow Moonstone”, Labradorite, Spectrolite, etc.