Many people dream of striking it rich by finding a nugget of gold in the wild. While that might be a long shot, it’s not impossible. Gold can be found in a few different types of rocks.
To determine if a rock contains gold, you can perform several non-destructive tests. A few of these include scratching the surface against unglazed ceramic and performing a magnet test.
Sedimentary rocks
If you’re looking for gold, sedimentary rocks tend to hold the most of it. This is because gold is released from igneous and metamorphic rock by weathering and erosion, then deposited in rivers or other streams. Sedimentary rocks that contain the most gold are granite, schist, and sandstone. These types of rocks are formed by the accumulation and deposition of fragments of other rocks, as well as organic materials like plants or animal shells.
The earliest known gold deposit was found in sedimentary rocks, which have been dated to 2.5 billion years old. This was in the Archean greenstone belt, which was a volcanic-sedimentary sequence that includes ultramafic rocks, dolerite, basalt, sandstone, shale, and chert. It is also possible to find gold in other types of sedimentary rock, including quartz veins.
To find gold in sedimentary rock, it’s important to know where and how to look. The best places to look for gold in sedimentary rock are alluvial deposits and granite. Alluvial deposits are characterized by eroded rock that is washed away by water. Granite is an excellent rock to look for because it is able to trap the gold that’s washed down from hillsides and mountains. Look for a yellowish color and a metallic luster in these rocks to see if they are gold-bearing.
You can also find gold in metamorphic rocks that are derived from sedimentary rock. These rocks are formed when the underlying sedimentary rock is changed by high temperatures and pressure. Coal is one example of a metamorphic rock that contains gold. It is a black rock that is very soft and crumbly. Another metamorphic rock that contains gold is schist. This is a type of metamorphic rock that contains micas that sparkle in the sun.
Lastly, sulfide-rich metamorphic rocks are another good place to find gold. These rocks are rich in pyrite, realgar, and arsenic sulfide. These types of rocks are a good place to look for gold because they can form in layers that make it easy to spot. The sulfides in these rocks are also very common, which means that they are likely to be easy to extract.
Igneous rocks
Gold occurs in igneous rocks such as granite, basalt and obsidian. It may be found in veins of quartz or in the coarse base metal sulfides such as pyrite and galena. Unlike sand and gravel, gold does not easily wash out of these types of rocks but tends to remain in them until they are weathered, metamorphosed or eroded away. Identifying gold in rock is often difficult, but it can be identified by a light-yellow streak and by a magnet test. Iron pyrite (fool’s gold) is magnetic and will stick to the magnet; real gold does not.
The composition of igneous rock can tell geologists much about the conditions under which it formed. Igneous rock forms when magma erupts from the surface of the Earth, or is injected into the ground by melting in the mantle, or is cooled as it oozes slowly to the Earth’s crust. The chemistry of the magma determines what minerals crystallize to form the different rock types. Light-colored magma, for example, will yield rock with high proportions of lighter silicate minerals such as quartz and feldspar; dark magma will produce rock rich in iron and magnesium sulfides like pyroxene and olivine. Rocks whose color falls between these two are known as intermediate.
Igneous rocks can contain large amounts of gold, especially when they have been subjected to metamorphic conditions that reduce their particle size. These conditions usually require heat and pressure, although if they are low enough, temperatures alone will suffice. Minerals such as calcite, syenites and micas are common in metamorphic igneous rock. These rock types can be a source of gold when they are deposited in river valleys, where they are rounded up by glaciers and transported downstream to form placer deposits.
Gold can also be found in greenschist, a metamorphic rock derived from igneous rocks such as basalt and gabbro. This is a relatively rare occurrence, though, as it is difficult to metamorphose rocks without sufficient heat and pressure.
Quartz
The mineral quartz consists of silicon dioxide (SiO2). It is a common mineral that forms in sedimentary and metamorphic rock. It occurs in various colors and is often twinned or distorted. The crystals can be faceted for gemstones and are also used as window glass and in electronics. Quartz is one of the most abundant minerals in Earth’s continental crust. It is found in nearly all geologic environments.
Gold in quartz is not common. Gold is normally associated with other materials and is only passed onto quartz if the conditions are right. It is therefore important to recognise signs that indicate a potential gold-bearing lode. Quartz floats are a good indicator of gold-bearing material, as well as quartz veins. In quartz veins, gold is typically found in contact zones with other minerals such as pyrite and chalcopyrite.
It is also possible to find gold in a quartz swarm. This is a group of small fragments of quartz that have been dislodged from other rocks by erosion or faulting. These can be found in metamorphic rocks such as schists and granites, and have been identified with gold in several areas worldwide.
Whether gold is present in a quartz swarm or in a quartz vein, the most reliable way to identify it is by chemical analysis or by panning. Gold in quartz is usually elemental, and is easily spotted with the naked eye. The best specimens are hand cut and polished to create a unique piece of jewelry.
A rare opportunity to own a piece of gold within this beautiful milky Quartz crystal. The gold is visible on both the front and back sides of the quartz. There are small pyrite crystals included in this Quartz specimen as well.
Gold in quartz is most common in veins formed when porous bodies of host rock are changed by replacement to form gold ores. These are typically associated with fault zones that act as conduits for mineralizing fluids. In some cases, these veins have been altered by rock deformation to make them more ductile and brittle. This allows them to withstand crushing forces and the fracturing that can accompany the movement of the fluids which have replaced them. These structures are often found in metamorphic and igneous rock.
Slate
Slate is a fine-grained rock forming when sedimentary rock such as shale and mudstone undergoes metamorphism. The resulting rock is usually gray but may be other colors such as purple, green, and blue. It is also known for the way it breaks into splinters that can be used for roofing and flooring. This property is due to the rock’s foliation and lineation.
Gold can be found in slate, although it is not very common. In fact, it is more likely to be found in igneous rocks such as basalt or schist. When you find a slate that seems to have gold in it, there are several ways to test for its presence. You can use a magnet to see if the gold is magnetic, or you can look for the mineral pyrite, which has a metallic luster and resembles fool’s gold. You can also look for signs of hydrothermal activity, such as hematite and limonite.
Most slate is formed from shale, which is a sedimentary rock made up of clay minerals. When the shale is buried, heat from deep in the Earth and magma changes its clay minerals to mica and chlorite. This change is called low-grade metamorphism. Downward pressure causes the mica and chlorite to reorganize themselves into layers. These layers are then compressed to form the slate.
In addition to the mica and chlorite, slate can contain quartz and feldspar, as well as other minerals such as biotite, calcite, hematite, pyrite, apatite, and tourmaline. It can also be a very dark rock, often with streaks of red, or even black.
The color of slate varies based on the location from which it is mined and the degree of metamorphism that it has undergone. In general, the darker slates owe their color to carbonaceous material or iron sulfides. The bluish and purple varieties of slate are typically rich in hematite, while the green variety is mainly composed of chlorite.
Slate is a popular rock for roof tiles, as it can be very durable and attractive. The fact that it can be broken into thin sheets means that it can be used for other purposes as well. Gold is rare in slate, but it can be found in many other types of rocks as well, including gneiss, schist, and granite.