Ammolite- Natural Versus Capped.

When purchasing Ammolite gemstones or jewellery, the words ‘Spinel Capped’ or ‘Natural’ frequently crop up.

But what exactly does this mean?

On the Mohs hardness scale, the gem layer of Ammolite is somewhere between 4.5-5.5, this is comparable to ‘Fluorite’ or the Famous ‘Blue John’ from the North West of England.

Though by no means the softest mineral, Ammolite still renders it’s self quite unusable in it’s natural form for everyday wear and tear in jewellery as it is very easily scratched.

The way around this problem is to fit a clear cap on to the Ammolite gem layer at the cutting stage.

Usually, the clear cap is simply a Cabochon of Spinel that is cut to the same size of the Ammolite layer and then bonded into place using resin, any overhang of the cap is then trimmed flat against the sides of the Ammolite and the gemstone is then complete.

As the spinel cap has a mohs hardness of 8. the Ammolite stone is now usable in jewellery and can quite easily stand up to the daily wear and tear that an item of jewellery can encounter.

The actual mohs scale looks like this:

1. Talc (such as soapstone, used for carving)
2. Gypsum (used to make plaster)
3. Calcite (commonly found as Stalactites & Stalagmites in caves)
4. Fluorite (Ammolite fall’s around this mark)
5. Apatite
6. Orthoclase (also known as moonstone)
7. Quartz (the most abundant mineral on the planet, Amethyst, Tigereye, Aventurine etc.)
8. Topaz (the spinel cap fall’s here)
9. Corundum (Ruby and Sapphire are both corundum)
10. Diamond (the hardest natural material)

Occasionally, clear Quartz caps are used in place of Spinel, these (quartz) caps tend to be cut deeper and lack the clarity of Spinel and are therefor usually reserved for lower grades of Ammolite or for unusual and non-calibrated shapes and sizes of Ammolite stones.

So, as a general rule of thumb, if Ammolite is purchased as a collector piece and destined never to be set in an item of jewellery, then a ‘Natural‘ piece is preferable. However, if the Ammolite is to be made into a ring, pendant or a pair of earrings etc. Then a capped (either spinel or quartz) is the safest option.

Ammolite Natural Ammolite Triplet

 

What is Ammolite?

Ammolite is the rarest of gemstones, even rarer than diamond, it was discovered in the 1960’s in Canada (Alberta). The colourful ‘fire’ that ammolite gives off is unique to each stone so no two are ever the same. At this present time, the only place that ammolite is mined is in Alberta, Canada. And sources say there is only enough ammolite left in the mine for the next 15-20 years so the value is only set to go up and up.

How is Ammolite formed ?

Ammolite is approximately 70 million years old and is formed from a rare, mineralized fossil called an ammonite. Ammonites looked like giant Chambered Nautilus shells. Ammolite has been formed by the compression and alteration of ammonite shell. Only two species of ammonite produce gem material: Placenticeras meeki and intercalare. These ammonites are found in the Bearpaw Formation (Upper Cretaceous) which extends over a large part of Alberta into Montana, Wyoming, and the Dakotas. Gem quality material is only found in the area between the Red Deer River and the Milk River in southern Alberta. Ammolite is a multicolour opaque gemstone which resembles “boulder opals”. Gem quality ammolite is a crushed sheet of ammonite shell preserved in the centre of ironstone concretions.