AMETHYST – mineralogically speaking

spirit quartz amethyst

Originally published on Tumblr and FB in February of 2018

Don’t we all love amethyst?  I know I do.  And February is definitely the month to celebrate our love of amethyst! This beautiful birthstone is a semi-precious gemstone.  It actually used to be one of the Cardinal Gems, along with diamond, ruby, sapphire, and emerald. This elite group are termed “precious gemstones”.  With the abundance of sources to find amethyst, it is now considered semi-precious along with all the other gemstones. Oh bah – they are all precious to me, don’t you agree?

Amethyst is a variation of quartz (silicon dioxide, or SI2).  Whenever quartz is violet, it is Amethyst. So, mineralogically and most correctly, you would write “Quartz, var. Amethyst” on a specimen card.  We don’t need to get that formal, but it is a good point!   Amethyst can appear in a wide range of purples, from pink to ALMOST black. When looking at a beautiful amethyst, you may also see the secondary blue hues and, rarely, the red hues. (*This is not the same opaque red that is exhibited with the inclusion of Hematite.)  

The thing to note is this:  If it isn’t purple, it isn’t amethyst.

MINERALOGICALLY, HOW IS QUARTZ, var. AMETHYST, FORMED?

Amethyst is a mineral that is formed in metamorphic or igneous cavities when the conditions are right.  The violet colouring is due to IRON.  

When amethyst is formed, the water that enables the crystal growth carries dissolved ferric (Fe+3) iron, becoming part of the structure of the crystal as it grows and forming what are known as “colour centers”.  Natural radiation in the ground then strips an electron from the ferric iron atom, activating the colour center and giving amethyst its violet colour.  The intensity of the colour is directly related to: 1. how much iron is present, and 2. where it is located in the atomic structure of the quartz crystal.  There is also an hypothesis that when aluminum is present, a smoky colour can result.

“DIFFERENT” COLOURS OF AMETHYST Gemstones, in general, receive their colour due to impurities.  Often, different colourings of amethyst are sold as ‘coloured amethyst’.  I personally do not do this, as I like to call things what they really are.  There is certainly a massive amount of information online and in published books that will describe certain powers of these treated, and often very low quality, stones.    Do you think it might be so they can sell it to you?  

HEAT TREATED AMETHYST Here is an awesome photo of natural dark purple amethyst together with three other heat treated samples to compare side by side. Thank you mindat.org for providing photo.

Top right:  18w low pressure UV mercury lamps for 3 months.  Initially the colour loss was rapid, but slowed down over time.

Bottom left:  380 degrees Celsius for 8 hours, most violet colour is gone  and some of it has started to turn yellow

Bottom right:  450 degrees celsius for 12 hours = no violet colour and an orange-brown colour that appears intensely and close to the surface.

When heat treating amethyst, some of it will actually turn green instead. Instead of discarding it, they sell it to you as “Green Amethyst”

PRASIOLITE: It is a rare stone in nature, which is why it would command a higher price.  Big surprise – the rock industry saw an opportunity and decided to use the heat treated amethyst that turned green by marketing and selling it as Prasiolite. The more correct term for Prasiolite is green quartz, or Vermarine.

It is incorrect to call it Green Amethyst!

Natural prasiolite is a very light, translucent green. Darker green quartz is generally the result of artificial treatment.

BLACK AMETHYST” is real amethyst with some hematite inclusions.  This gives the amethyst an almost black tint.  when you look at it through a strong light, you will see that it is a very dark violet.  If it is actually black, then it is not amethyst.  It would be considered Morion Quartz. (Remember: Amethyst=Violet.)

AMETRINE is a type of quartz that exhibits both the violet amethyst and the yellow of citrine. The colour of the zones visible within ametrine are due to differing oxidation states of iron within the crystal. These occur due when there is temperature gradient across the crystal during its formation.  This is another form of amethyst that is more often heat treated than not (*if it’s more expensive, it’s more likely to be natural ametrine).  Most jewellery items stating “Ametrine Gemstone” have been heat treated or irradiated, and if the price isn’t costly, it is likely synthetic.

LAB GROWN AMETHYST is grown using hydrothermal methods and compares in colour to the highest grade samples found in nature.  It is hard to differentiate it from natural amethyst without advanced gemmological testing.

RED AMETHYST” should more appropriately be named Hematoid Quartz.  Remember, if there is no violet colour, it is not amethyst.  Red Quartz is the result of hematite being included as the ‘impurity’ that gives the quartz its red colour.

So, there is a brief summary on Amethyst and some of the mislabelled quartz out there.  Tomorrow, I will provide information on the many healing uses of Amethyst Quartz.

Until then, what do you like the BEST about Amethyst??

Written by Dawn Markus, Master of Crystology

Owner of Crystal Rockin Mineral Shop#amethyst blackamethyst greenquartz prasiolite greenamethyst hematoidquartz amethystspiritquartz howisamethystformed cardinalgemnomo

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