The goal of this Earthcache: educate visitors about the difference in Granite, Gneiss, and Greenstone as well as the potential composition of veins that may appear in rocks. All answers can be found by looking at the rock at GZ and reading the cache page.
Logging Requirements: you (or a member of your group) must send answers to the 4 questions below in a message or email to the owner using the link at the top of the page and each cacher must include a photo with their log (task 5 below).
1. The large rock at GZ has parallel lines running in the same direction, which direction are the lines running (vertical, horizontal, or diagonal)?
2. What colours are present in the large rock and what do you think caused these colours?
3. Based on your answers to 1 and 2 what type of rock are you looking at? (Note: one of the three rocks described on the cache page - granite, gneiss or greenstone)
4. There is a very noticable vein running through the rock. Provide an estimate of the vein thickness, what colour the vein is, and what type of vein you think it is.
5. To prove you were at GZ , include a photo of yourself or some other identifying item at GZ including the rock in the background. You do not need to show your face in the photo.
Granite, Gneiss, or Greenstone?
Granite is a coarse-grained, felsic intrusive igneous rock primarily composed of quartz, potassium feldspar, and plagioclase feldspar, with minor amounts of mica or hornblende. Formed by the slow crystallization of magma deep within the Earth's crust, it is a hard, durable stone known for its speckled, light-colored appearance and granular texture. Typically light-colored (pink, white, grey, beige) with interlocking, visible mineral crystals.
Gneiss is a type of metamorphic rock. It starts with rocks formed from volcanoes (igneous) or rocks made of sand and mud (sedimentary). Then, it gets squeezed and heated deep inside the Earth and can change (metamorph) into gneiss. This rock is formed under pressures ranging from 2 to 24 kbar, sometimes even more, and temperatures over 300 °C (572 °F). The banding is developed at high temperature when the rock is more strongly compressed in one direction than in other directions. The bands develop perpendicular to the direction of greatest compression, also called the shortening direction. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands. It is a metamorphic rock composed of mineral grains easily seen with the naked eye, which form obvious compositional layers, but has a weak tendency to fracture along these layers. The minerals in gneiss are arranged into layers that appear as bands in cross section. The darker bands have relatively more mafic minerals (such as magnesium and iron). The lighter bands contain relatively more felsic minerals (light-colored, low-density silicate minerals rich in silica, aluminum, sodium, and potassium, primarily comprising quartz, feldspar, and muscovite).
Greenstone is a dense, dark green, low-grade metamorphic rock formed by the alteration of dark-colored volcanic rocks (like basalt). Composed primarily of green minerals like chlorite, actinolite, and epidote, it features a fine-grained texture with a green, grayish, or black hue.
Veins in Rocks
Veins in rocks are geological formations where minerals precipitate out of a solution (dissolved substances in a liquid solution aggregate to form an insoluble solid) within fractures or cracks in the host rock. These veins can vary in composition, size, and formation mechanism. They are extremely common in all rock types igneous, metamorphic, and sedimentary, and serve as indicators of past fluid flow.
Four Veins commonly found in rocks:
1. Quartz: Quartz veins are one of the most common types of veins in rocks and are often white, milky, or clear, and can be quite thick or thin.They consist primarily of quartz, often with minor amounts of other minerals such as pyrite, calcite, or fluorite. Quartz veins can form in a variety of geological settings, including hydrothermal veins, shear zones, and faults. Common in both metamorphic and igneous rocks.
2. Calcite: Calcite veins are composed predominantly of the mineral calcite (calcium carbonate).These veins often form in sedimentary rocks, limestone, and dolomite, but can also occur in igneous and metamorphic rocks. Calcite veins are commonly associated with fractures and faults.
3. Sulfide: Sulfide veins contain minerals such as pyrite (iron sulfide), galena (lead sulfide), chalcopyrite (copper iron sulfide), and sphalerite (zinc sulfide). These veins are often associated with hydrothermal ore deposits.
4. Barite: Barite veins consist primarily of the mineral barite (barium sulfate). These veins commonly occur in sedimentary rocks, often associated with hydrocarbon deposits. Barite veins can also form in hydrothermal systems.