The Red Stripe Test
I won't discuss the survey that was done at Roehampton School Cave on April 3, 2004, here, but I will talk about the RED STRIPE TEST.
In the Roehampton School Cave, we saw these strong bedded layers of brown rock. This rock seemed to be more resistant to erosion than the other limestone. So what was it? As a caver, you don't carry a laboratory with you to analyse rocks, so we have to be inventive.
But first let me tell you something about the hardness of rocks and minerals. What is hardness? It is the resistance of the surface of a mineral or rock to scratching. All right, what can we do with it? Now, depending on the chemical composition, each mineral has a well determined hardness. Early in the nineteenth century, there was that clever man, Mr F. Mohs, from Austria, who made a hardness scale based on a series of ten fairly common minerals. The softest mineral got a number one and the hardest a number ten. So, here we have as an amateur mineralogist a very nice tool to check what mineral or rock we have in our hands.
If for instance our unknown species of mineral can scratch Calcite but can't scratch Fluorite then the hardness of this specimen must be between 3 and 4. But we normally don't carry those minerals with us and do we need all those different hardnesses? No, because as a caver you will mostly see rocks based on Calcite or on Quartz. So we need a reference material somewhere between hardness 3 and 7. And what is very abundant throughout the island? The Red Stripe Bottle!! These multifunctional bottles have a hardness of 5.5!!
The different steps of the RED STRIPE TEST!!!
We took some specimens of the brown rock in Roehampton School Cave. When you break this rock, the inside is white. The brown colour is only a very thin patina on the surface. The Red Stripe Test showed us that the mineral was harder than the bottle. Also the typical resinous luster and conchoidal fracture gives a certainty of 99.99 % that this rock is indeed Flint. This mineral is a subvitreous form of quartz (silica) which has a hardness of 6.5.
Limestone which is almost pure microcrystaline Calcite has a hardness of 3, so doing the Red Stripe Test with a piece of limestone would give a powdery line on the bottle which we can wipe off without any scratch.
JCO Articles and Advisories