This EarthCache is a disabled friendly and child friendly experience, with a level path which is suitable for wheelchairs, buggys and prams. So, what are we here to look at? We are here to look at a lump of quartz which forms part of the wall. More specifically, we are here to look at the crystals that form part of the quartz. The idea behind this EarthCache is to make the cacher look more closely at the geological features.
What is quartz?
Quartz is the second most abundant mineral in the continental crust. It is a defining constituent of granite and other felsic igneous rocks, and is very common in sedimentary rocks such as sandstone. While the majority of quartz crystallizes from molten magma, much quartz also chemically precipitates from hot hydrothermal veins, sometimes with minerals like gold, silver and copper. It is formed from silicon and oxygen. One of the most important distinctions between types of quartz is that of size, and colour.
Macrocrystalline, is when individual crystals are visible to the unaided eye. The microcrystalline or cryptocrystalline varieties are aggregates of crystals not visible to the naked eye.
The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Some macrocrystalline (large crystal) varieties are well known and popular as ornamental stone and as gemstones.
Crystal shapes.
There are different types of crystal shapes.
Cubic : These are like a dice.
Hexagonal : These can be long pointed crystals, with six sides.
Botryoidal : These are rounded 3 dimensional crystals.
Acicular : These are needle like.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile. The specific rock is indicated in the below picture.
1. Would you describe the crystals as macrocrystalline, microcrystalline or cryptocrystalline? Why have you come to this conclusion?
2. Looking at the crystals, what type of crystal can you see here? Please describe them, in terms of colour and crystal shape.