[Geography Notes] on Agate Pdf for Exam

Natural agate is a glassy, colourless, variety of microcrystalline quartz. The agate gemstone is used as a semiprecious stone when it is of appealing colour and quality. Agate is a diversification of chalcedony, a cryptocrystalline type of quartz. Translucency, patterns of colour, or moss-like inclusions may differentiate this stone from other types of chalcedony. Agates can display a huge variety of vivid, multiple colours. These are primarily an outcome of traces of oxides of iron, chromium, titanium, manganese, nickel, and other elements.

Formation of Agate

Agate evolves in a huge range of colours, which include white, red, pink, grey, brown, black, and yellow. The colours are brought about by impurities and take place as alternating bands within the agate. The different colours were induced as ground waters of various compositions discharged into the cavity. The banding within a cavity is a record of change in the chemistry of water. This banding provides different agates with the interesting patterns and colours which makes it a popular gemstone.

Agates are usually formed by the accumulation of silica from groundwater in the cavities of igneous rocks. The agate accumulates in concentric layers around the walls of the cavity, or in horizontal layers structuring from the bottom of the cavity. These structures create the banded patterns which are characteristic of many agates. Some of these cavities are fringed with crystals and those are called geodes.

Different Varieties of Agate

The colour patterns in agates generally acquire the form of flat or concentric layers or bands. Mossy or dendritic inclusions can occasionally imitate similarity to landscapes and vegetation. Varieties of this gemstone are primarily described by their colour patterns, source and/or inclusions. Let’s check out the various types of agate:

1. Banded

With regular colour layers and bright colours, this variety is the most prominent. These stones can be found all around the world, however, Brazil is one of the most productive and proficient sources. Many of the affluently coloured, banded agates you spot for sale are dyed.

2. Moss, Plume, and Dendritic

These stones consist of mossy inclusions of mineral oxides which may be any colour. Stones that reflect plant-like patterns are known as moss agates. Those with tree-like, branch patterns are known as dendritic agates. Those with feather-like patterns are known as plume agates.

3. Lace

Known for their delicate design, these stones are banded with complex loops and swirls. Mexico is one of the premier sources of lace type of agate.

4. Picture or Scenic

Some inclusions can create the impression of whole landscapes, complete with lakes, trees, shrubs, and shorelines within an agate. Stones that depict these “natural beauties” are highly treasured.

5. Fire

Inclusions of plate-like crystals of limonite make fire agates scintillating and shimmery. Cutting and polishing can further amplify this effect.

6. Iris

These stones display iridescent colours casting back from between the colour layers.

7. Shell

Embedded, silicified shells develop patterns in these agates. Turritella agate is made up mainly of shells and shell fragments of the gastropod turritella and several other species.

8. Petrified Wood

Fossilized primitive tree trunks and limbs may contain their organic compositions replaced by agate stone over millions of years. In a few instances, their woody structure may also be conserved and observed with a microscope. The agate’s colour may be very deep, sharp and bright.

Agate Enhancements

How are agates enhanced? Dyeing is an ancient and most prevalent practice for enhancing agates. (Chalcedony stones are comparatively porous). This is generally a stable procedure. A commemorated secret procedure for dyeing agates was developed in Idar-Oberstein, Germany, in the 19th century. When the agate accumulations in this town were consumed to exhaustion, migrants to South America shipped grey agates back to Idar-Oberstein. These pieces were dyed and the outcome was remarkable. However, dyeing enhancements must be revealed to consumers.

Refer to the table below to find out the sources of agates.

Sources of Agates

Agate Stone Sizes

Agates are generally nodular, but masses can be some pounds and many inches in diameter.

Indian Agate  

Quite popular, the stone of immortality, Indian Agate, draws attention to the idea of growing old with ever spiraling inner beauty, intellect, and respect for all that is and has been. Scientifically, the Indian origin agate is known to aid in getting relieved of old emotions and attracting a positive outlook on life. The red in Indian Agate promotes innovation, influential and willpower.

Eye Agate                      

Agate Eyes are commonly found in Agate nodules, which are generally developed when silica precipitates in the rock cavity. These cavities are akin to lava flows, fractures in the rock layers, or fossils that have solvated over time. Agate Eyes shows one or more concentric markings which are called to be eyes.