Starting from the very basics, a crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an ordered pattern extending in all three spatial dimensions. In addition to their microscopic structure, large crystals are usually identifiable by their macroscopic geometrical shape, consisting of flat faces with specific, characteristic orientations.
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystallineliquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array of points repeating periodically in three dimensions. The points can be thought of as forming identical tiny boxes, called unit cells, that fill the space of the lattice. The lengths of the edges of a unit cell and the angles between them are called the lattice parameters. The symmetry properties of the crystal are embodied in its space group.
A crystal’s structure and symmetry play a role in determining many of its physical properties, such as cleavage, electronic band structure, and optical transparency.
There’s more than one way to categorize a crystal! The two most common methods are to group them according to their crystalline structure and to to group them according to their chemical/physical properties:
Crystal Grouped by Lattices (Shape)
There are seven crystal lattice systems:
- Cubic or Isometric – not always cube shaped! You’ll also find octahedrons (eight faces) and dodecahedrons (10 faces).
- Tetragonal – similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms.
- Orthorhombic – like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together).
- Hexagonal – six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon.
- Trigonal – possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.
- Triclinic – usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.
- Monoclinic – like skewed tetragonal crystals, often forming prisms and double pyramids.
This is a very simplified view of crystal structures. In addition, the lattices can be primitive (only one lattice point per unit cell) or non-primitive (more than one lattice point per unit cell). Combining the 7 crystal systems with the 2 lattice types yields the 14 Bravais Lattices (named after Auguste Bravais, who worked out lattice structures in 1850). The structure of real crystals is pretty complicated! You can read about crystallography and mineral structures here and here.
Crystals Grouped by Properties
There are four main categories of crystals, as grouped by their chemical and physical properties:
- Covalent Crystals
A covalent crystals has true covalent bonds between all of the atoms in the crystal. You can think of a covalent crystal as one big molecule. Many covalent crystals have extremely high melting points. Examples of covalent crystals include diamond and zinc sulfide crystals.
- Metallic Crystals
Individual metal atoms of metallic crystals sit on lattice sites. This leaves the outer electrons of these atoms free to float around the lattice. Metallic crystals tend to be very dense and have high melting points.
- Ionic Crystals
The atoms of ionic crystals are held together by electrostatic forces (ionic bonds). Ionic crystals are hard and have relatively high melting points. Table salt (NaCl) is an example of this type of crystal.
- Molecular Crystals
These crystals contain recognizable molecules within their structures. A molecular crystal is held together by non-covalent interactions, like van der Waals forces or hydrogen bonding. Molecular crystals tend to be soft with relatively low melting points. Rock candy, the crystalline form of table sugar or sucrose, is an example of a molecular crystal.
As with the lattice classification system, this system isn’t completely cut-and-dried. Sometimes it’s hard to categorize crystals as belonging to one class as opposed to another. However, these broad groupings will provide you with some understanding of structures.
Crystals Throughout History
The use of crystals has a long documented history and has been present in practically every culture and religious tradition. Below are some history tidbits for people who are interested in reading more about the history of crystal use. The history tidbits below are not meant to be a comprehensive history of crystals, but rather they are just meant to give a small sample of how prevalent the use of crystals has been throughout history and across the world.
Crystal History Tidbits:
-The healing uses of crystals are documented as far back as 1500 B.C. in the Ebers Papyrus from Egypt. This Egyptian medicinal text documented the many ways in which crystals were used for healing.
-The ancient Egyptians strongly believed in the healing and protective power of crystals. Many pharaohs wore crystals on their headdresses and many crystal amulets have been found in their tombs. The pharaohs often had their masks lined with crystals in the belief that crystals helped them be better rulers. Many objects of Amazonite and Lapis were found in King Tut’s tomb and Amazonite was one of the stones on his famous gold mask.
-Crystals are also used for healing in Chinese Medicine, which dates back to at least 5000 years. Crystal needles are also often used in modern day Chinese acupuncture and in Pranic Healing.
-Crystals have also been recognized for healing by Tibetan Buddhists and the Ayurvedic healing system for hundreds of years. The use of crystals is popular in both Hinduism and Buddhism.
-The Vedas, sacred texts in Hinduism that are over 5,000 years old, thoroughly discuss the power of crystals and their uses for healing. The Vedas prescribe specific crystals for certain ailments and describe the properties and powers of different crystals. For example, in the Vedas it is written that Emeralds bring good luck and well-being.
-Crystals are referred to over 200 times in the Bible.
-As an example, in the Old Testament, the High Priests were required to dress in “holy garments,” which were centered around the Breastplate of the High Priests. God instructed Moses to build the Breastplate of the High Priests and gave him step by step directions as to the twelve crystals he was to include on the Breastplate.
-In the New Testament, God’s heavenly city, New Jerusalem, is said to be built on foundations of crystals. “And the building of the wall of it was of jasper: and the city was pure gold, like unto clear glass. And the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; The fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.”
-In 1150, Saint Hildegard wrote two medical treatises where she documented the healing properties of crystals and their uses. She described how the vibrational energy in crystals strengthened the weak and healed illnesses. Saint Hildegard was highly regarded for her many accomplishments. In the 1100’s she wrote poems, books on medicine and theology, plays, and composed music, on top of being a nun, physician, orator, scientist, preacher, consultant to popes and kings, and a philosopher. She also founded two monasteries. These accomplishments would be amazing for a woman today, let alone a woman living in the 1100s.
-In Muslim culture, using the power of crystals has also been very popular. The Muslim prophet, Muhammad, himself wore a Carnelian ring and it was believed by many that wearing a Carnelian ring guaranteed Allah granting all your desires, which made Carnelian a very popular crystal amongst Muslims.
-Excerpt from Jameel Kermalli’s book, “Islam: The Absolute Truth”:
“In Islam, a tradition states that Ali used to wear four rings on his hand – Opal (Yaqut) for beauty and dignity; Turquoise (Feruz) for obtaining divine help and victory; Hadid Thin for strength, and Carnelian (Aqiq) to protect himself from enemies and all types of misfortunes. The religion Islam has strongly recommended its followers to wear rings made from different stones, as a way to increase faith, piety, and endurance. The stones of Aqiq, Feruz and so forth have been specifically recommended by the Prophet (S) himself to wear them at all times, and especially during prayer. Stones have unlimited practical and medicinal properties.
….’Aqiq protects Shia from unjust rulers and from everything else, which causes fear.’ (Amali of Tusi – Volume 1, Page 36)
This means that the stone recognizes a Shia of Ali and produces strong energy fields that block adulterated nearby sources of energy. This is why Muslims have been advised to keep their rings in one place at all times when they are not wearing the stones – this way the energy that is absorbed and released from such stones surround themselves within the stone.”
Random History Tidbits on Specific Crystals:
-The use of crystals for healing was very popular amongst indigenous tribes across the world.
-The Mayans used the power of crystals for healing on physical, emotional, mental, and spiritual levels. They also used crystals to diagnose diseases.
-The Incas also used crystals for their power and healing. They particularly regarded the Emerald as a very powerful, holy stone and it is said that many Incas chose to die rather than give the conquerors the location of their Emerald mines.
-The medicine men in many Native American tribes and indigenous tribes in Australia also used (and still use) crystals to diagnose illnesses, as well as to heal people.
-“For the Middle Ages and even into the 17th century, the talismanic values of precious stones were believed in by high and low, by princes and peasants, by the learned as well as the ignorant.” (George Frederick Kunz, in his book “The Curious Lore of Precious Stones”)
– Tibetan monks considered quartz crystal spheres to be holy objects of great powers.
-Taoists called quartz the “gem of enlightenment.”
-In Japan, quartz crystal spheres were considered to represent the heart of dragons and in Japanese culture, dragons symbolize power and wisdom.
-Cleopatra’s favorite piece of jewelery was said to be an Amethyst ring, engraved with the figure of the Persian Sun god, Mithras. Since she seduced two powerful Roman generals, Mark Antony and Julius Caesar, it was believed by Roman wives that wearing Amethyst would ensure the devotion and faithfulness of their husbands.
-St. Valentine was said to wear an Amethyst ring carved with a picture of Cupid.
-Alexander the Great was said to wear a large Emerald during battles to ensure victory.
-The Moguls of India, including Shah Jahan (who built the Taj Mahal), took Emeralds, inscribed them with sacred text and wore them as talismans.
-In Buddhism, the Medicine Buddha is called “Healing Master of Lapis Lazuli Radiance,” and rituals involving the Medicine Buddha include meditating on Lapis Lazuli.
– The ancient Sumerians valued Lapis as the most sacred stone. The ancient Sumerian Priests had a popular saying, “He who carries with him into battle an amulet of Lapis carries with him the presence of his God.”
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