1. History of the Mineral Agate
2. What Exactly is Agate?
3. Agate Stone Different Varieties
4. A Few More Agate Facts
5. Agate Healing Properties
6. Article Photos
7. Our Collection of Agate
8. More Information
History of the Mineral Agate
The mineral agate was highly valued by many ancient cultures including the Sumerians, Egyptians, Greeks and Romans. The stone was widely used for talismans, seals, vessels (container used mainly for liquids), beads and gemstones. One of the oldest of all minerals, references to agate can be traced back more than two thousand years to the writings of Theophrastus. The process of describing different varieties of agate can be found in his works Theophrastus On Stones in which this Ancient Greek philosopher (c.370 - 285 BC) compares the hardness of agate stone to onyx and talks about how one variety of agate can differ from the other because of "its irregular and uncertain manner of spots, clouds and variegations". He says that although agate stones are predominantly grey, different colours can be present and are often beautifully spread out. Patterns may resemble trees, shrubs, plants, clouds, rivers and even animals. He goes on to say the ancients separated agates into different varieties giving each one a name that highlighted its difference from the "common agate". That difference could be colour, markings or texture.
Red coloured agates were known as haemachates the prefix "haema" coming from the Greek word for blood with reference to its colour. The name achates as the stone was known at the time came from the name of a river in Sicily where the mineral was first discovered. In reference to the discovery Theophrastus wrote; these stones have been found to exist in almost every nation on Earth. Those which featured patterns resembling trees and shrubs were called dendrachates (from the word dendrite) whilst other varieties were "idly named" according to the powers they held or even because of the stone's similarity in colour to animal skin.
The Ancient Roman author, naturalist and natural philosopher Pliny the Elder (23 AD - 79 AD) also wrote about the mineral agate in his works "Naturalis Historia" and frequently made reference to Theophrastus' work.
Achates was a stone formerly in high esteem, but now held in none. It was first found in Sicily, near a river of that name; but has since been discovered in numerous other localities. In size it exceeds any other stones of this class, and the varieties of it are numerous, the name varying accordingly.
He goes on to name several different types of agate and the locations where they can be found. Like Theophrastus he also makes reference to dendrachates (dendritic agate) which he says is "marked with small shrubs". Dendritic agate stones are included with dendrites which are crystals with a branching formation that can often resemble plants or other organic matter. Pliny talks about different agate stones from India and their distinctive markings and says "the sight of some is beneficial for the eyes whilst others when held in the mouth allay thirst. Then there are those which are good for counteracting the effects of poison inflicted by the scorpion. Agates can also be found in Cyprus."
He believed that agate with uniform colour would render athletes invincible and went on to say the stone with the highest value had the transparency of glass.
Crazy Lace Agate | Natural History Museum Los Angeles
What Exactly is Agate?
Agate is a translucent variety of the mineral chalcedony made up almost entirely of silicon dioxide also known as quartz. The stone often occurs in shades of black, white and grey but can also be exceptionally colourful. Any colour and banding that's present is the result of trace impurities of other minerals.
The quartz crystals present in agate are colourless in their purest form but turn red or brown with the presence of iron, pink with manganese or dark green with chromium. Other geological factors including light and heat often in the form of radiation also play a part in defining colour.
Some would argue that to be classified as a "true" agate the stone must must exhibit banding but there are several varieties which do not exhibit this characteristic at all. Over the years there have been endless discussions regarding the accuracy of the names of certain rocks and minerals and it's safe to say that some are highly likely from a geological perspective to have been named incorrectly or are at least misleading. Having read and written about rocks and minerals for many years, my advice would be not to look too deeply into the name of a stone.
Moss and dendritic agate stones are two varieties that don't exhibit any visible banding but feature curious inclusions known as dendrites. Often mistaken for organic matter, dendrites are crystal formations similar to those seen on glass during winter and are caused primarily by impurities of iron and manganese. Dendrite comes from the Greek word for tree and refers to a "branching form". Stones that feature dendritic inclusions can sometimes be mistaken for fossils.
Although frequently found within igneous rocks the mineral agate can also occur in other rock types as well. Its formation begins when ground water containing silica (sand or quartz) that has entered the rock through holes dries up leaving behind a residue of minerals. As the process repeats multiple layers of minerals build up within the rock following the outline of the cavity and once full, the entire mass begins to crystallise. Quartz crystals often grow in any space left unfilled and when their tips point towards a void, the structure becomes known as a geode.
The cavity containing the crystallised minerals is known as a nodule. Depending on the rock type it can be incredibly resilient to weathering and will often survive long after the host rock has eroded. The agate formation will remain securely locked away until the nodule is found and broken open.
On Mohs scale of mineral hardness agate stone grades 7 so it's quite a hard material which makes it relatively easy to work with.
Smithsonian Museum Washington D.C. Photo; Stone Mania
Agate Stone Different Varieties
Although often characterised by concentric, curved or angular banding the mineral agate can also exhibit other curious and often intricate patterns. Hundreds of different varieties of this stone can be found around the world and many have their own unique names. These often indicate the locality where it's found or a particular colour or characteristic.
Fortification agate is a generic name for the stone whose bands are arranged at sharp angles. The name stems from the shape which was once believed to resemble the lines of a fortress. A fortification is a defensive wall or other reinforcement built to strengthen a building against attack. Blue lace and crazy lace are both types of fortification agate. Botswana agate comes from Botswana, Brazil agate from Brazil, fire agate exhibits a distinctive flash of colour caused by inclusions of hematite and polka dot agate often but not always features distinctive spots. Agatized dinosaur bone despite its name is not actually an agate. The word "agatized" is simply a description of the process that has taken place because the organic matter in the original cell structure of the dinosaur's bone was slowly replaced with the mineral agate.
Natural History Museum Los Angeles
A Few More Agate Facts
During biblical times the mineral agate was believed to have been the second stone in the third row of the high priest breastplate. This religious garment adorned with twelve precious gemstones was worn by the Jewish high priest whilst presenting himself to God.
Agate is a stone that's dependant on the presence of other minerals for its colour so also occurs naturally in black, white and grey. These colours are often not considered to be sufficiently appealing to the wider commercial market so stones are often dyed. The practice of dying rocks and minerals is nothing new and can be traced back thousands of years. Agate has long been known to be porous with the ability to hold dyes particularly well and it can sometimes be difficult to determine whether a stone's colour is really natural.
Despite everything that has been learnt about the formation of agate there's still a great deal that's not fully understood. The stone's formation from start to finish has never been studied in real time and it has not been possible to recreate the mineral in a laboratory environment so much of what is known is supposition.
Agate stone is associated with the star sign Gemini and is the traditional birthstone for the month of May.
Agate Healing Properties
The mineral agate is a grounding stone so will bring the emotional, physical and mental into balance. Being grounded is important because it helps us to remain calm, rational and make better decisions especially when surrounded by chaos. Agate is soothing and calming and harmonizes positive and negative energies. It works at its own pace but is powerful yet gentle. Stones may be used to bring information to the surface that's deeply rooted in the subconscious and can help rebuild self-confidence.
An ideal stone for enhancing concentration, agate can improve analytical ability and help find practical solutions to difficult situations. Agate encourages the truth to be seen and spoken and helps deal with negativity and bitterness especially in relation to love. It can heal anger and resentment and give courage to make it possible to start over again.
A powerful healing stone on both a mental and physical level, agate can dissolve stress and tension which makes it a good companion for use during meditation.
The agates in the first three and the last photograph in this article are courtesy of Stan Celestian on Flickr. Clicking any image on this page will redirect to the original full sized photo.
Our Collection of Agate