Amethyst- January 2019 Mineral of the Month
MINERAL OF THE MONTH – AMETHYST
· Mineral: Quartz variety Amethyst
· Chemistry: SiO2
· Class: tectosilicate
· Crystal system: Hexagonal-Rhombohedral
· Color: violet to purple
· Refractive index: 1.54 to 1.55
· Luster: vitreous
· Specific gravity: 2.65
· Mohs Hardness: 7.0
· Cleavage: none
· Fracture: conchoidal
Taos Rockers mineral of the month is the violet to purple variety of quartz known as Amethyst. The name amethyst comes from the Greek "a-methystos", (α-μεθηστos) which means “not drunk”/ "not intoxicate", a reference to the belief that the stone protected its owner from drunkenness. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Amethyst is a semiprecious stone often used in jewelry and is the traditional birthstone for February.The bible mentions amethyst as one of the twelve stones in the breastplate of the High Priest. Amethyst was considered one of the Cardinal gems, one of the five gemstones considered precious above all others, until large deposits were found in Brazil.
The coloration is attributed to gamma irradiation and the presence of traces of iron built into its crystal lattice. The irradiation causes the iron Fe+3 atoms that replace Si+4 in the lattice to lose an electron and form a [FeO4/Metal] color center. The coloration is typically unevenly distributed in the individual crystals. Coloration in Smoky Quartz is also attributed to gamma irradiation and trace ions and explains the presence of both smoky zones and amethystine zones within the same crystal. When amethyst is heated above 600°F it turns yellow, orange or brown and then resembles the quartz variety citrine. Prolonged exposure to sunlight (UV irradiation) will also slowly fade the color centers.
Amethyst can be found in many diverse environments, but is mainly associated with igneous rocks and pegmatites. Amethyst crystals longer than 12 inches are very rare. The most common growth forms are:
Druzy crystal aggregates which outline cavities; the crystals are usually short-prismatic and often lack prism faces. Most common in volcanic rocks, but also in hydrothermal veins, and even in cavities in sedimentary rocks.
Scepters (late syntaxial overgrowth) on other color varieties of quartz, in particular in high- to medium-temperature environments like alpine-type fissures and pegmatites
Split-growth crystals ("artichoke quartz") in hydrothermal veins in ore deposits, but also in volcanic rocks.
As individual well-formed crystals in small cavities and fissures, in particular in volcanic rocks.
As hydrothermal vein filling, often with several growth phases with variable color that cause a banding pattern.
Some of the mineral locales from which specimens of Amethyst are available at Taos Rockers include:
Rock Currier, in an article on Amethyst appearing on mindat.com (https://www.mindat.org/article.php/905/Amethyst+Specimens) says the following:
There are certainly well over a thousand localities in the world that have produced amethyst specimens of varying quality. The most prolific locality in the world for amethyst specimens and agate nodules is found in Rio Grande do Sul, the southernmost state of Brazil.
This region produced amethyst and agate during the last part of the 19th century, all during the 20th century and is still going strong. The total production of the area can be measured in kilotons. Knowledgeable individuals place the current production of amethyst specimens at two to three thousand tons a year.
The geology of the region is mostly sheet basalts weathered into a rich, green farming area. Sheet basalts are rock formations that form when cracks in the earth open and molten rock pours out over the earth’s surface like a big thick blanket. Each flow can be a few feet to over a hundred feet thick and can cover many thousands of square miles. Some of these flows occur again and again, building up over time to depths of many thousands of feet. Basalt is an igneous rock and in Southern Brazil is black to gray on a fresh break. Some of the basalt flows in Rio Grande do Sul are rich in gas and form gas bubbles that are trapped inside basalt flows when they cool and harden into rock. In Rio Grande do Sul the size of the bubbles (vesicles) ranges from microscopic to several feet in diameter (less than 3 meters) and as much as five or even six meters tall. These vesicles tend to be typically rounded, and taller than they are broad. They are somewhat flat on the bottom, and usually taper to a narrower rounded top, very much in shape like the cone heads of television sitcom fame. Sometimes these cones become distorted along one or more axes or run together and occasionally vesicles with two or more “cone heads” are found. If these can be taken out intact, which they usually are, they are cut in half along the long axis of the geode and form half "cone heads" which are commonly called amethyst cathedrals.
Melody, in her book Love Is In The Earth, says: “Amethyst is a “stone of spirituality and contentment”, a “stone of meditation.”“It opens and activates the crown chakra…It clears the aura and stabilizes and transmutes any dysfunctional energy located within ones body…Amethyst, overall, assists in the assimilation of new ideas.”