The next gemstone on our list of feldspar might be more obscure compared to the ones already introduced, though it is no less outstanding! It is the orthoclase!

History and Meaning

Orthoclase was first named “orthose” in 1801 by Rene Just Haüy after the Greek word “orthos”, meaning “right”. Eventually, Johann Friedrich August Breithaupt changed it to “orthoklas” in 1823, with the new “klas” syllable being based on the Greek word “klasis”, or “cleavage”. It is a reference to the double cleavage planes that form a right angle. Unfortunately, being a less well known gemstone, it does not have much of a history unlike the other feldspar gemstones.

Colours

It comes in generally paler colours like white, greenish white, grayish yellow and pale pink. It can also be colourless. The yellow orthoclase are the ones often seen in jewelry.

Properties

Orthoclase has a hardness of 6. Like other feldspar gems, it can easily be scratched or cleaved when used as jewelry so it has earned a reputation of being a collector’s gemstone rather than a jeweler’s gemstone. 

Unlike most other feldspar gemstones, it is a partially ordered variety of potassium feldspar rather than a plagioclase feldspar. In terms of molecular structure, it is nestled between the more random arrangement of sandinine and the ordered microcline. 

Location

Orthoclase appears in all kinds of rocks like igneous rocks (cooled magma). Large crystals of it can be found in a type of igneous rock called pegmatite. They can also be found in the other rocks like sedimentary (weathered rocks) and metamorphic (altered from other rocks). The yellow orthoclase used as gemstones are found mainly in Madagascar.

Fun Facts

A typical orthoclase is more known for its widespread use as a raw material for commercial production of glass and ceramics rather than jewelry. A special type of orthoclase that is very popular as jewelry actually exists under another name. It is called a moonstone, famous for its blue adularescence! Jewelry aside, orthoclase is also one of the most abundant rock forming minerals in the earth’s crust!