What are the different types of crystal structures in Minerals?

 1. Introduction


2. Crystals in Minerals


3. How to Determine if a Mineral has Crystals


4. How Crystals Are Formed.


5. How to Determine if a Mineral has Crystals


6. Classification of Crystals in Minerals
  • Euhedral crystals
  • Anhedral crystals
  • Subhedral crystals
7. The Six Basic Crystal Structures In MInerals 
  • cubic System
  • Tetragonal System
  • Hexagonal System
  • Orthorhombic System
  • Monoclinic System
  • Triclinic System
8. Conclusion




1. Introduction

What do all minerals have in common? You may be thinking, “a crystal structure.” While that is certainly true, there’s more to it than just the arrangement of atoms. Depending on certain factors such as the mineral’s chemistry and physical properties, a wide variety of minerals can form crystals. If a mineral does not contain a crystal structure, it might still be considered crystalline because of its molecular geometry. Or if it doesn’t have molecules that are arranged into a three-dimensional space, the mineral is still considered crystalline. In fact, some definitions even include minerals without crystals (such as amorphous quartz).


Types  Of Crystal Structures In Minerals, Pyrite
pyrite Crystals

2. Crystals in Minerals


Minerals are naturally occurring and are part of the rock formation. These comprise Earth’s crust, lithosphere, and deeper parts of the mantle. Minerals occur in large amounts as well as subtle amounts on every continent with approximately 10,000 different species found in nature. Although they are more visible than organisms in their natural state (as diamonds on sand or dust), they still need to be cleaned to view their full beauty and sparkle. Crystals can be found within certain minerals and even though most are not visible to the naked eye, you may find that once the mineral has been cleaned and polished, you begin to see an outline.

Types  Of Crystal Structures In Minerals
Minerals

3. How to Determine if a Mineral has Crystals

If you want to be sure your precious stones have crystals on them, the simplest way to check is by shining a bright light through them. A magnifying glass will work as well, but it's easier to inspect a crystal under a strong light source. Other methods include testing with a refractometer or using a special camera lens to check off-center crystals; however, these can be expensive and time-consuming. Crystals are a beautiful, fascinating group of minerals that have fascinated people since ancient times. Crystals can be simple (like salt or quartz) or complex (like diamonds ). This guide focuses on the most common types of crystals


Types  Of Crystal Structures In Minerals: Quartz light passing through the mineral
Quartz Crystals 

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4. How Crystals Are Formed.


Crystals form in a wide variety of ways. For example, when water percolates down through soil filled with tiny particles of silica quartz those silica grains will sometimes grow into crystals. When tiny inclusions of metal like iron pyrite (fool's gold) get trapped between layers of crystal growth, these metal atoms will crystallize along with the silica grains into a mineral known as pyrite minerals. "Why do crystals have such a unique structure?" The answer has to do with how atoms join together and bond to form molecules. In the case of a solid mineral, individual atoms usually join together in the same crystal plane, forming a three-dimensional structure. There are many different ways that atoms can bond, and this is what causes crystals to take on different shapes. The relationships between these bonding atoms are what make up the molecular framework of a solid mineral.


Types  Of Crystal Structures In Minerals, Anhydrite mineral structure
Anhydrite Crystal Structure

 5. Classification of Crystals in Minerals


Crystals are the skeletons of minerals. They are made up of atoms in a regular pattern and are composed of many different kinds of atoms. There are many different crystal structures, including:

  • Euhedral crystals


Euhedral crystals have regular, geometric shapes formed by the arrangement of atoms in a lattice structure. For example, a diamond is a euhedral crystal.


Types  Of Crystal Structures In Minerals: pyrite mineral
Pyrite Crystals



  • Anhedral crystals


Anhedral crystals have irregular shapes that lack a well-defined shape because the arrangement of atoms is disorganized or not even. For example, quartz has an anhedral structure.

Types  Of Crystal Structures In Minerals: petrographic Quartz mineral
Quartz Crystal Under Petrographic Microscope

  • Subhedral crystals


Subhedral crystals have features or defects that scatter or weaken the bonds between atoms to make them less regular. For example, graphite has a subhedral structure.

Types  Of Crystal Structures In Minerals: graphite, pencil, metamorphic mineral
Graphite Mineral


7. The Six Basic Crystal Structures In MInerals 

Scientists have identified six basic crystal structures. These are: Cubic (three-dimensional), Hexagonal (six-sided), Tetragonal (four-sided), Orthorhombic (two-dimensional), Monoclinic (single crystal) and Triclinic (three-dimensional).

  • cubic System


The cube is a perfectly symmetrical structure with all its faces of equal size. The center face of a cube can be divided into two smaller cubes called a checkerboard or a cross-shape. It's also common for one side of a cube to be longer than another; this causes a truncated pyramid to develop on one side but not on another.

Types  Of Crystal Structures In Minerals: Cubic Crystal system in mineral, with nodes and lattice structure
Cubic Crystal  System
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  • Tetragonal System


The tetragonal crystal system is the most common and includes diamonds, amethyst, and quartz. The tetragonal crystal system is the only one that has four symmetrical axes. This system is stable but not very common. Tetragonal crystals have four axes: those of the faces, the bases, the vertices, and the corners. Tetragonal crystals have four sides and a tetrahedron at their center, divided into four equal sections by four parallel planes. 

Tetragonal  Crystal System
Tetragonal Crystal System

  • Hexagonal System


Hexagonal crystals have six sides and an equilateral triangle at their center, divided into three equal sections by two parallel planes. These crystals have rounded ends like hexagons. They're easy to recognize because they're symmetrical around their corners and edges they don't have any sharp points

Hexagonal  Crystal System
Hexagonal Crystal System

  • Orthorhombic System


The orthorhombic crystal system is a rarer structure, They have two parallel planes that meet at 90° angles. This kind of crystal is also called rhombohedral because each atom is arranged in four directions (rhombs) or "H"s. These kinds of crystals include amethysts, agates, jade, kyanite, tourmaline, and zirconium. 

Orthorhombic Crystal System:amethysts, agates, jade, kyanite, tourmaline, and zirconium.
 Orthorhombic Crystal System

  • Monoclinic System


Monoclinic crystals have a beautiful symmetry about their center point, making them a popular choice for jewelry and tableware. The monoclinic crystal system includes mica, barite, and fluorite.

Monoclinic Crystal System
Monoclinic Crystal System

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  • Triclinic System


The triclinic lattice is formed by three axes of equal length. It's used in the unique mineral peridotite and in some kinds of petrified wood. The triclinic crystal system includes garnet, quartz, and pyrite.

Triclinic Crystal System
Triclinic Crystal System

8. Conclusion


Crystals come in many different sizes, shapes, and forms. Learning about the different types of crystals structures in minerals can help you identify them when you are out on a hike. Crystals are made up of a specific regular, repeating internal arrangement of atoms, ions, or molecules in three dimensions. They have characteristic forms based on their structure and external symmetry elements.


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