WHAT ARE THE DIFFERENCES BETWEEN AGATE AND JASPER Both agate and jasper are chalcedony minerals. To clear up any confusion, there is a light blue mineral called chalcedony. The chalcedony family, however, refers to quartz based minerals that are microcrystalline or cryptocrystalline in structure. (The words microcrystalline and cryptocrystalline mean the same thing and are often used interchangeably). Like quartz, chalcedony minerals have a hardness of 7. Chalcedony minerals tend to have a smooth and waxy feel / luster which make them excellent candidates to be cut and polished for gemstone jewelry. Chalcedony minerals come in most colors with the most common being white, gray, yellow, orange, red, brown and black. The designs / patterns on chalcedony minerals are also varied. MICROCRYSTALLINE AND MACROCRYSTALLINE Microcrystalline quartz are quartz based minerals (SiO2) whose crystal structure can only be seen through strong magnification. This is because the size of the crystals are smaller than 30 microns (one micron is 1 / 1000th of a millimeter). Other microcrystalline quartz are bloodstone, carnelian, chalcedony and chrysoprase. Macrocrystalline quartz, on the other hand, refers to quartz with a crystalline structure that can be seen by the eye or a simple lens. These include clear quartz, smokey quartz, amethyst, rose quartz, citrine and ametrine, all of which are translucent or transparent. TRANSPARENT, SEMI-TRANSPARENT, TRANSLUCENT AND OPAQUE MINERALS Transparent - light and images can be seen through the mineral Semi Transparent – images may appear distorted or foggy through the mineral Translucent- a small amount of light can be seen through the mineral (generally through the thin edges) Opaque - inability of any light to pass through the mineral AGATES AND JASPERS CAN BE DIFFICULT TO TELL APART Agates and jaspers are sometimes difficult to distinguish from each other because they can contain primarily the same minerals. WHAT ARE AGATES Agates are translucent or semi transparent chalcedony. Agates are known for their bands, however agates can also have dendritic, mottled, moss or plume like patterns. Sometimes the bands on agates are larger than the crystal itself, being hard to see / identify the concentric bands. Such is the case with carnelian. By and large, agates are translucent or semi translucent. HOW DO AGATES FORM Agates usually form in areas of volcanic activity and water. The water in those areas contains a high content of silica which flows through the cavities and crevices of the igneous rock. The most common of these igneous rock are basalt, rhyolite and andesite. If the silica water has a particularly high concentration of dissolved silica, a silica gel can form on the walls of the rock openings. Eventually, that gel crystallizes into microcrystalline quartz. As more time goes by, additional layers of the gel form creating “younger” bands of microcrystalline quartz on the walls of the fractures and cavities. During this time, it is very easy for impurities to creep into the silica mixture. This is how the agates get their coloring, banding and other patterns. Agates can also form inside sedimentary rock, such as limestone. Both igneous and sedimentary rocks are extremely vulnerable to weathering… much more so than the durable agates. So, when weathering eventually erodes the host rock, the agates remain. This is the reason why agate nodules are often found in water streams that are around igneous or sedimentary rocks. WHAT ARE JASPERS Jasper is an opaque variety of chalcedony. Opaque means if you hold it up to a light source neither light nor images will come through it. Jaspers can also be banded or striated depending on how they form. In its pure form, microcrystalline quartz is semitransparent. When impurities or foreign materials grow within the crystal, it changes its color and ability to transmit light. The high amount of impurities in the jasper is what makes them opaque. Agates tend to be translucent because they contain less impurities and foreign materials than jasper. HOW DO JASPERS FORM Jaspers generally form in areas where there is fine, soft sediment or volcanic ash. Over time, the silica rich mixture begins to combine and “cement” the sediment into a solid mass. The varying sediment and ash are what gives jasper its many colors and patterns. Weathering also plays an important role in the beautiful colors and patterns. The first two pictures are agate and the last two pictures are jasper.
Posted on: Fri, 05 Sep 2014 21:37:00 +0000
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