Gold

Mineral Name: Gold

Chemical Composition: Au

Color: Golden yellow to brass yellow

Streak: Golden yellow

Hardness: 2.5 to 3

Cleavage/Fracture: Golf has no cleavage pattern but it does have a fracture pattern. Hackly fracture can be seen on its jaggedy and also sharp surfaces.

Crystal Form: Gold is isometric, meaning it comes in many different forms such as: cubic (which resembles a third-dimensional square); octahedral (which looks like two pyramids that are glued to the base); cuboctahedral (which looks like six stop signs glued together to for a cube, but with the open areas sealed so it is like an 8-bit volleyball), tetrahexahedral (which is a form that can resemble a cube with very low pyramids at each end, for a total of four faces on all six sides, making the shape almost spherical but it has twenty-four faces) (3).

Gold can also show twinning. The Spinel-Law Twin is another crystal structure and this one takes place when two octahedral crystals form at the base in a sort of twin-like fashion. Gold can also form a Triangular Contact Twin, which is the result of sharing a single face on the starting octahedron. This face can be distorted or weathered on an octahedron and will turn the rhombus into a pancaked-triangular prism with smaller faces around its edges, giving it more faces. This means gold can be found in many different variations. Lastly, gold can also be found in flakes and nuggets, and can even sometimes be alloyed with or mixed in with materials like silver or copper (3).

Luster: Metallic

Special Features: Gold is malleable, resists tarnish, conducts electricity, can be worn for long periods of time. It is biocompatible, edible, and potentially contains healing properties dating back to China 2000 BC. It was used to treat smallpox and even remove mercury from the skin and flesh (5).

Varieties: Gold can be found in a variety such as Electrum Gold, which is naturally alloyed with silver and copper (3). There is also gold leaf, which is gold beaten into incredibly tiny sheets and is often eaten or used to decorate buildings with significant value.

Mineral Group: Gold belongs to the native elements, which is a group of minerals that only consist of one element. Minerals belonging to the native elements include diamond, sulfur, copper and gold. Gold is belongs to the metallic and semi-metallic alloys, which are groups containing two metallic or semi-metallic elements together varying in percentages (3).

Environment: When gold is in a flowing magma or is in a subduction system that is creating magma, like the subduction of the Juan de Fuca plate boundary with the North American plate, gold-bearing magma and is concentrated into the mountains where it cools and can later be mined.

Associated Rock types: Gold ore is the main rock type in which gold can be found, which is mainly associated with veins related to igneous processes. Gold can be a component in the metamorphic rock albatite (6).

Occurrence in North America: There was a large event in US history called “The California Gold Rush”, which happened in the late 1800s which brought lots of people in search of gold due to the media and other news exposing the exciting discovery. Additionally, gold can be found in Alaska and has multiple tv shows dedicated to it. Other states where gold is found in large quantities is Nevada, South Dakota, and Colorado (3).

Economic Uses: Gold is one of many currencies dating back about 6,000 years ago when it was used to complete trades (5). In today’s society, gold is rarely ever used to complete transactions but some national-organizations may have gold saved as investments. With gold being able to conduct electricity, many businesses will try to stock up in it to create their electronics. For instance, there is approximately 0.035 grams of gold in each cell phone (5). Many electronics use gold, but also use better conductors like copper and silver (5).

Industrial Uses: Gold is used as wiring in electronic devices because it can conducts electricity and it does not tarnish (1). Dentist used the mineral in the 1500’s for filling rotted away cavities in teeth, and gold is still being used today for crowns in dentistry because of the minerals bio-compatibility (1). Gold is also used in jewelry and can be worn for any period of time without causing any kind of irritation to the skin or any disease (1).

First Notable Identification: Gold has been used since the ancient Egyptians, and gold objects have been excavated from Egyptian tombs that are more than 5,000 years old (1). Gold has the symbols Au on the periodic table of elements for Aurum, or Gold, in Latin (1).

How We Identified It: You can identify gold by its bright gold color and gold streak.

Don’t Confuse It With: Gold is often confused with pyrite; however, pyrite can break fairly easily and is brittle. Gold is malleable, so it bends. Also pyrite will leave a black streak and not gold-yellow streak like gold. People in movies also bite into gold to prove it is gold because it is much softer than pyrite.