Rocks as Gems

The word “rock” doesn’t normally conjure up images of beautiful jewelry, but as I explained in my very first blog post (https://mochisgifts.com/2014/06/05/gem-vs-mineral/), some rocks are also considered gems. While many minerals meet the criteria of beauty, rarity, and durability to be considered gems, very few rocks do.

Because the conditions under which rocks form can vary greatly, there can be very different looking results. Even within a specific type of rock, although the main mineral components are the same, trace elements or other minerals, sizes of individual grains, relative amounts of each mineral, and more, may differ. Causes for these differences include: the elements available in the melt source, temperature, and pressure. Most of the rocks used as gems have individual minerals that are visible to the naked eye, but some, such as basalt (sold as “lava”) have mineral grains too small to see. This variability is part of the beauty of the rock, but can also make it very difficult to match pieces for jewelry.

Enjoy these examples of rocks that are gems – I’ve listed the main constituent minerals.

Lapis lazuli

Blue: lazurite
Brassy/gold: pyrite
White: calcite

Ruby in zoisite

Green: zoisite
Red: ruby
Black: hornblende

See my blog: https://mochisgifts.com/2019/07/03/ruby-in-zoisite/

Tiger Iron

Gray: hematite
Gold: tigers eye
Red: jasper

See my blog on hematite: https://mochisgifts.com/2014/10/17/hematite-synthetic-hematite-and-disclosure/

Unakite

Green: epidote
Pink/orange: potassium feldspar
Gray: quartz

Lava (basalt)

Individual grains too small to see but include:
Plagioclase feldspar
Pyroxene minerals
Olivene
and many other accessory minerals

Graphic Granite

(labeled as “feldspar” when I purchased it)
Gray: quartz
White: feldspar
and many other accessory minerals

So yes, we geologists love rocks, but now even non-geologists have a reason to enjoy them too!

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