CAN YOU NAME THESE AGATES? These are two of the most easily recognised agates. Most likely the silica impregnated this rock after layers of silt had already formed. The rose quartz stone on the right is formed from a mass of visible rose quartz crystals, and the bottom stone from near Port Alberni lacks the translucency of an agate and could be called jasper as it has some silica in it (see the white quartz patch?), but obviously contains a lot of other minerals to make it opaque and multicoloured. It’s an agate because it’s made of quartz (cannot be scratched by a penknife), is translucent, shows some banding (the outer layer is a lighter colour than the inner one) and no visible crystals can be seen within the bands although visible crystals line the cavity inside the nodule. WHICH OF THESE STONES IS AN AGATE? The answer is the top left stone, which is a broken nodule of carnelian (because of its orange-brown colour) agate from Oregon. Obviously, your average rockhound can’t see the microscopic arrangement of quartz crystals, so most identify agates by intuition, experience, and convention, which is what we will do here. There has recently been an attempt to define an agate more scientifically, with the suggestions that a true agate has its microscopic quartz crystals arranged in fibres, whereas these crystals in jasper, chert and flint are granular. The general name for cryptocrystalline quartz is chalcedony (pronounced kalcedony ), and non-banded forms coloured by small amounts of certain minerals are give special names, such as carnelian (orange due to iron impurities) and chrysoprase (green due to nickel impurities) although carnelian showing banding may also be considered an agate. To complicate matters further, translucent quartz stones without banding are often called agates, and any rock or fossil with a high level of cryptocrystalline quartz is often said to be ‘agatized’. However, the distinction between agates and jaspers and other rocks can be blurred some jaspers have patches of banded agate, and many of our opaque local rocks that are called jaspers have rather little silica compared to the famous ‘porcelain’ jaspers found in the U.S. Agates are usually recognised by being translucent with distinct bands, while jaspers, flint and chert generally do not show bands and contain high levels of minerals that make them more opaque. This means that the quartz is in the form of ‘micro crystals’ that cannot be seen with the naked eye. WHAT IS AN AGATE? Agates, like jasper, flint and chert, are made of cryptocrystalline quartz (silicon dioxide = silica). So here is a short quiz and some pointers of what to look for. Quartz is also the main constituent of a wide variety of stones that we’ll cover in a moment.Cowichan Valley Rockhounds Agates are my favourite stones to collect, cut and polish, and even new rockhounds can recognise some of the more distinctive agates with relatively little knowledge. It’s commonly used to power watches and in audio sensors, where its unique properties can really shine. Quartz also displays a strong piezoelectric effect due to its structure. The crystals are also favored among those who believe in the healing power of stones. Rock crystal has been used to make everything from sculptures to crystalline plates and bowls. Quartz has a long history of use, and not just as jewelry. Some crystals are double terminated, meaning they have a point on both ends. Quartz crystals are usually hexagonal, with six sides and a terminated point resembling a pyramid.
The crystal formations are visible to the naked eye, unlike cryptocrystalline forms of silica like chalcedony or jasper. Quartz is a macrocrystalline form of silicon dioxide(SiO₂ or silica). For many collectors, that’s an important distinction. In other words, it’s wholly synthetic and it really only appeared on the market in the late 1990s.Īnytime you see a “new” variation of quartz available do your research. Instead, these stones have a thin layer of gold or titanium deposited on their surface. It’s a pretty, iridescent piece of quartz but it’s not natural in the slightest. In addition to treated specimens, collectors will also find “mystic quartz” available. Natural stocks of the stuff are low and the vast majority is heat-treated or irradiated to bring in the characteristic olive hue. Other stones are almost always treated, such as prasiolite. In formations like clusters, the stones will often have a “burnt” look to their coloration, with the deep orange even fading into brown at some points. Since they’re chemically identical, you usually have to judge based on how the colors look.
0 kommentar(er)
