GAG26: Friend or Foe EarthCache

This cache has been placed for the GAG26 event, which starts on October 26th, 2018 at 6:00 PM.

Good morning 007,  British intelligent just learned that the evil organisation Mineralio is developing a new evil weapon. They have their best minds Prof. Calcite and Prof. Quartzite working day and night on it. MI6 just received a coded note that one of them is ready to switch sides and tell us all of Mineralio secrets. Your mission is to infiltrate Mineralio and rescue the RIGHT brilliant Chemist.  To help you in your Mission Q has prepared the following Document

How to tell the Difference between Quartzite and Calcite

Quartz and Calcite are common minerals that exist in rocks all around the world. Both minerals form in a variety of colors, such as purple, white, brown, gray and colorless, which at times makes them appear similar. However, these two minerals have many distinctively different physical and chemical properties that differentiate them.

You can perform a few simple tests in order to tell who is who

Chemical Composition

Quartzite or Quartz is a chemical made from silicon dioxide crystals (SiO₂) while Calcite is composed from calcium carbonate (CaCO₃). They may look the same but will react differently with acids. While Quartz will not react with acids such as HCl, Calcite will dissolve with contact with acids. Recent experiments done by MI6 showed that vinegar is not strong enough, but lemon juice (15-20 mL )can work and you should see some gas formed according to this equation (don’t worry its very local and won't damage the rock).

2H⁺ + CaCO₃ -> CO₂(gas)+H₂O+Ca²⁺

Hardness Test

According to the Mohs scale of mineral hardness Quartz has an hardness of 7 while Calcite is only a 3 (Dimond is a 10), this means that Quart can scratch calcite but calcite can not harm quartz. This is all fine but how can you test that in the field? Do you have a set of keys on you? Try to scratch the sample and see if you can make a mark: If you did its calcite if you cant its quartz.

Crystal Shape

Quartz and calcite crystals have distinctively different crystal shapes. Everyone recognizes the hexagonal prism shape of a quartz crystal. A perfect crystal will look like a pencil with a sharp tip. Sometimes the tip is not a hexagonal pyramid but a 3 edge one. Calcite is different its most common form is a rhombohedron (tilted or slanted cube), though it also can form prismatic crystals, scalenohedrons, and other less common forms and combinations. 

Cleavage and Fracture

Cleavage is a crystal's ability to break along weak bonds within the crystal structure. The break results in a smooth surface. Calcite exhibits rhombic cleavage, which means that it breaks along three planes of weakness that create a rhombic shape for the crystal (like we talked about before). Quartz does not have strong cleavage but can fracture across the crystal, leaving a rough surface on the broken crystal. Quartz fractures are described as conchoidal when the fractured surface exhibits a swirl pattern on the stone.

Its Operation GAG26 Time

Alright, 007 I think you are equipped with all the knowledge, gather all the equipment you need and remember the Queen is counting on you.

Stage 1: (Posted coordinates)

Our friends at the MOSAD provided us with a test site to practice your technique.  You will find 3 big boulders one of them is unique. Use any of the tests you choose (or all of them) and see if you can determine who is it Quartzite or Calcite ?

Stage 2:

This is our only shot to recognize who is the Prof. that sent us the note. He said he hide some clues in the rocks that will point you in the right direction. Which one is our friend and which one is our enemy?  Prof. Quartzite or Prof. Calcite ?