Water from a stone?

There’s an old saying that’s often used to describe something that is difficult. It goes along the lines of “it’s like squeezing water from a stone”.

In most cases, this is true.

Unless we mimic pressure and temperature conditions that exist deep in the Earth, here on the surface, squeezing a rock and having water come out is a bit laughable.

But when it really happens…when you crack open a rock and get splashed? That is cause for some excitement in the lab!

Hand holding a rock with a cavity.

Finding water in a rock is an extremely rare occurrence. This photo shows the Aris phonolite that was broken open to expose a fluid-filled miarolitic cavity. Image: Paula Piilonen © Canadian Museum of Nature

A vial with a small amount of clear liquid next to pieces of split rock.

Once broken open, the fluid within the cavities was collected with a syringe and deposited in a vial for future chemical analyses. Image: Paula Piilonen © Canadian Museum of Nature

There is a famous mineral locality in Namibia, the Aris quarry, known for the wide range of rare minerals found in the small cavities or pockets within the phonolite (an alkaline rock). The rocks there are 34 million years old.

One mineral collector casually mentioned that when they break open the rocks at the Aris quarry, they get splashed by water. I was both amused and confused at the same time.

Splashed? By water coming out of a rock? Surely this only happens after it has rained, correct?

No.

No??

Apparently this phenomenon is common—the water seems to be coming from the cavities in the phonolite, some of which can be up to 10 cm in diameter.

Water that has been trapped within the cavities for 34 million years? I was intrigued, to say the least!

First, let’s talk about magma. Magma is a mixture of a number of things: molten rock (liquid), small crystals (solids) and a variety of gases (water vapour, carbon dioxide, sulphur). When magma cools, minerals start to form out of the molten rock as well as crystallizing on top of the existing mineral crystals.

Minerals are formed from chemical components called elements. When magma cools, certain compatible elements tend to enter into the first minerals that are formed. Examples of compatible elements are silicon, iron, magnesium, aluminum, potassium and calcium. They bond together and create rock-forming minerals such as quartz, feldspars, pyroxene, amphibole, olivine and micas. These garden-variety minerals account for 99% of the Earth’s crust.

Collage: Close-up views of three mineral specimens.

Left: Arisite from the Aris quarry in Namibia. This new mineral species was described by museum scientists and named for the quarry where it was discovered. Top right: Makatite from the Aris quarry. Bottom right: Tuperssuatsiaite from the Aris quarry. Images: B. Lechner © B. Lechner

 

As the magma cools further, there are elements that do NOT want to enter the rock, remaining in the magma until the very end, along with the gases. We call these “incompatible” elements—strange elements such as zirconium, niobium, uranium, cesium, lithium, and the rare-earth elements.

Water, carbon dioxide and other gases also act as incompatible components. Incompatible elements are left behind in the magma, rejected by rock-forming minerals due to their size and/or charge. They form minerals only at the very last stages of crystallization.

Mineralogists LOVE incompatible elements! Why? Because they form rare mineral species—the <1% of the Earth’s crust that are the most interesting, for collectors and scientists alike.

When the magma that formed the phonolite at the Aris quarry started to cool, nepheline, aegirine (pyroxene) and feldspar crystallized first. As the magma cooled and solidified, the gases that were in the magma were allowed to escape and form gas + liquid bubbles. Minerals then crystallized within the bubble, or cavity.

In most cases, the gas and liquids within the cavity are all used up and the cavity is dry when cracked open millions of years later. In the phonolite samples we have from the Aris quarry, it appears that not all the liquid in the cavity was used up when the magma cooled.

Using a large rock splitter, we were able to crack a number of rocks open to reveal their liquid-filled cavities. Not often will you see mineralogists dancing in their lab, but if anyone had come near the prep lab on this day, they would have thought a party was happening. Actually opening up a cavity to find water is EXTREMELY rare—more rare than the proverbial needle in a haystack, and is certainly cause for celebration!

A man and a woman use a large rock splitter to break open rock pieces.

Mineralogists Paula Piilonen and Ralph Rowe using a rock splitter to break open pieces of Aris phonolite in order expose the fluid-filled cavities. Image: Glenn Poirier © Canadian Museum of Nature

By inserting a syringe into the cavity, we were able to capture the liquid and put it into glass vials for further analyses.

Is this original, 34 million year old “water” left over from the magma? Or is it water from the surface that leaked through the rock and filled the cavities? Here is where the real work begins—analyzing the chemistry of the liquid and discovering its origins. If it truly is 34 million years old, the resultant publication will certainly be a historic breakthrough. Results to follow!

About Paula Piilonen

A mineralogist with the Research Division at the Canadian Museum of Nature.
This entry was posted in Research, Rocks and minerals and tagged , , , , . Bookmark the permalink.

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