Quartz: the Series – Part 2

Don’t we all love crystals? the bigger the better?

Not always…sometimes the smallest things are of exquisite beauty.

Microcrystalline Quartz..the Wee Ones

Agates and Jasper are both fine example of Microcrystalline Quartz with spectacularly beautiful patterns and color.

Many people are asking …what is the difference between Agates and Jaspers?

Texture, baby…Texture

And what you may ask is ‘texture’?
Patterns of spheres, spots, banding and mineral alignment or layering.

Laguna Lace Agate

Agates are banded or show some sort of layering, like the one below…and often translucent.
Jaspers are opaque (no light will penetrate the surface) and are generally not banded

Some folks lump both jasper as a variety of agate. Not me, however…

Some agates are not exactly layered and some jaspers are somewhat banded. And some agates and jaspers have coarsely crystalline quartz within their tiny landscapes of micro-crystals.

Druzy Lace Agate

Like just about all else in Geology and life in general, the boundary is not razor-sharp but fuzzy and indistinct and we scratch or heads asking, “is it agate or is it jasper?”

One must learn to live with ambiguity.

 

By the way…those little circular textures in Lace Agate and Ocean Jasper are actually 3-dimensional spheres. What we see in the cut stone are cross-sections through the spheres. Overall, this texture is known to geologists as ‘botryoidal’, a term derived from the Greek word “botruoeidēs”, which means “bunch of grapes”.

Ocean Jasper

Lace Agate

It’s all Chalcedony...

Botryoidal Grape Agate

BUT, chalcedony need not be botryoidal, nor layered or banded. Nor is the botryoidal texture limited to chalcedony (e.g. Malachite, Hematite, etc)

So, where do these delicious chalcedony rocks form? Generally in weathering volcanic (e.g. Ocean Jasper…this article is a MUST! -if only for the drop-dead gorgeous pictures), and sedimentary rocks, whether or not the original rock had a lot of silica.
Occasionally chalcedony is found as a petrifying agent in fossils.

As in Dinosaur Bones…
At left is a “gemstone” dinosaur bone cabochon. In the Beginning, Dino bones were made of the same stuff as our bones—largely calcium. After death and extreme burial in the presence of silica and water, the calcium and other bone minerals are replaced with Chalcedony (the whitish and pinkish areas of the stone).

The image below is generally what a dinosaur bone looks like in a thin (30 micron) sections of a rock under polarized light. See Petrographic Microscope.

The image shows a “highly porous structure, with pores filled with late chalcedony, and the fossil remnants of the bone tissue, where black dots used to host a single bone cell. A larger void on the lower left was filled with fine quartz sand. Width of view: 5.3 mm.
Credit: Bernardo Cesare, Department of Geosciences, University of Padova, Padova, Italy”

Note: the cabochon of the gemstone dinosaur bone shown above is NOT the same rock as is shown in the photomicrograph, but the two are similar enough to show the chalcedony, regardless of the dino bone it replaced!

Chalcedony, of the Many Colored Flavors

All the agates and jaspers, plus the gemstones Carnelian, Aventurine, Chrysoprase, Onyx, Moss Agate, Dendrite

Rock on, everyone!

yours, in Quartz
-mary

Quartz: the Series

The α- Alpha  and the β- Beta

The Science & Art of Quartz.

SiO2

Our most beloved gemstone, in its myriad forms…Eleven crystalline and 2 non-crystalline minerals comprise silica (SiO2), though Quartz is the most common form. In our landscapes, in our lives…
Twelve percent of Earth’s surface is quartz, and a full 20% of the whole crust is quartz.

 

Geologists have plotted the various forms of SiO2  over the years, culminating in the diagram to the left.

MySiOinterests these days, and most of my life actually, lie in the blue and pink  areas on the diagram:  α-quartz and β-quartz, respectively.

α-Alpha and β-beta quartz occur in all igneous, metamorphic and sedimentary rock types. Within the alpha and beta fields lie a seemingly vast array of different rock types, all of which comprise quartz.

 

Beautiful enough for gemstones. Revered since antiquity. The ancient Egyptians were gifted artisans whose use of blood-red Carnelian—one of the Quartz gemstones—is iconic and legendary.

It’s ALL Quartz…

Trace elements (e.g. iron) produce the colors we see in all forms of Quartz, though it is not color but size and  translucency that are the keys to the Classification of Quartz.

From Large to Small…Macro to Micro to Crypto. Size matters not only in how quartz gemstones are classified, but how they come to display the endless and gorgeous variation in color and patterns of spheres,  bands and layers–whether smooth or crenulated. And why we love these humble stones more than diamonds.

Today, it’s all about Macro. Following are a few examples of the flavors of Quartz whose crystals are large enough to see without magnification. Tomorrow, the small stuff.

Macrocrystalline: Crystals are easily identified without magnification.

These Amethyst crystals are an example of Macrocrystalline Quartz.

The crystals do not have to be whole, perfect and complete like these. Some Quartz is quite coarsely crystalline yet do not display the crystal habit of the mineral.

 

 

Rose Quartz is a type of Macrocrystalline Quartz that does not form crystal faces, but is composed of many intergrown crystal ‘sub-individuals’

Citrine

Second most popular Quartz gemstone…Amethyst is first.

 

 

 

Ametrine

A naturally occurring variety of Macrocrystalline Quartz comprising zones of Amethyst intergrown with zones of Citrine.

 

 

 

Ametrine cut perpendicular to the c-axis of the crystal. Is that freaking cool or what???

 

Quartz crystal axes: 

Macro…Micro…Crytpo…it’s ALL Quartz.
Versatile, beautiful, ornamental

Carnelian Pendant wrapped in Copper wire.
(and yes, Carnelian is one of the many lovely flavors of quartz, of the Microcrystalline Quartz variety)

Find this and more or my work with the Gifts of the Earth here:
https://etsy.me/2Mobjji

And my Facebook page MCS Artworks

Thank you…

Coming Soon: Microcrystalline Quartz

 

 

References:
Ametrine    https://www.mindat.org/min-7606.html
Ametrine    https://en.wikipedia.org/wiki/Ametrine
The Mineral Citrine    https://www.minerals.net/mineral/citrine.aspx
The Mineral Quartz   https://www.minerals.net/mineral/quartz.aspx
The Quartz Page     http://www.quartzpage.de/crs_intro.html