Labradorite (sodium calcium aluminosilicate (Na,Ca)(Al,Si)4O8) forms in some basic igneous rocks such as anorthosite. It also occurs in some metamorphosed and sedimentary rocks. It occurs, for example, in association with olivines, pyroxenes, amphiboles, magnetite, chromite, ilmenite, chalcopyrite, pyrrhotite and pentlandite.
The largest deposits of labradorite are found in Canada, Finland and Madagascar (specimens are characterised by golden-green colour play and translucent stones with subtle bluish highlights). In addition, labradorite is also found in Australia (translucent labradorites of light and rye-brown colour), Mexico (transparent specimens), USA, Ukraine, Russia, Greenland, Italy, France, Romania and small finds in the Czech Republic.
It is used in the jewellery industry, where it is considered a valuable decorative stone. Labradorescent specimens are worked into cabochons or plates, and transparent crystals are sometimes cut into facets. The weight of cut stones is usually in the range of 10-20 carats, rarely exceeding 100 carats. Labradorite is also used to make beads, brooches, rings, cameos, small cases and other decorative items. It is also sometimes used as a carving material. Among the most sought-after varieties of labradorite are specimens with various iridescent colours, including red (spectrolite). Labradorite is also used in the ceramics industry and in antique joinery, where it is used as a facing material.
example of labradorite
Labradorite – detail
Labradorite is associated with a play of colours called labradorescence, a name made famous by the Danish geologist and mineralogist Ove Balthasar Bøggild. He defined it as "the peculiar reflection of light from submicroscopic planes oriented in one direction (rarely in two directions); these planes never have a position that can be expressed by simple indices and are not directly visible under the microscope". Light reflects and refracts on many crystals in different ways, and even on the same crystal, the reflection properties change when the viewpoint changes.
This effect arises in minerals composed of stacked layers that are slightly ‘out-of-sync’. Some waves of light collide with the first layer, immediately reflecting back, while others make it past the first layer only to be reflected by the next. This continues resulting in multiple waves that can constructively or destructively interfere with one another, generating a multi-layered, sometimes multi-colored, milky appearance.
But you can certainly test this for yourself when hunting.
To fulfill the logging requirements, you need to correctly answer the questions and send the results to me via E-Mail or GC message system:
1) What is the ratio between dark matrix and lighter crystal in this slab? Write down the ratio in x:y form.
2) Focus on one spot on the tilling and slowly change your perspective, how does the stone "change"?
3) Name and explain this phenomenon!
4) Make a photo of yourself (or your nick written on your hand or piece of paper) in front of the building so it is undeniable that it is in fact you. Add this photo to your log.
Logs that will not fulfill this requirement will be deleted.