Barite, Galena, Pyrite, Quartz, Rhodochrosite & Sphalerite
Barite is a barium sulphate mineral that occurs in many different colours and crystal shapes. It occurs in a variety of sedimentary and metamorphic settings and often replaces other minerals or fossils. Despite its many forms, it is relatively easy to identify because of its heavy weight. In fact, its name comes from the Ancient Creek “barys”, meaning heavy. Examples of different forms of barite include golden yellow honeycomb barite and Desert Rose barite that has a flower-like appearance. Barite is also often found in hydrothermal veins with ores of antimony, copper, lead, manganese and silver. Barite is used to add weight to oil and gas drilling fluids to prevent blowouts, as well as in paints and automotive parts, ceramics, LED TVs and medical applications. Geologists can analyze the oxygen and sulphur isotopes in barite to investigate ancient seawater compositions.
Galena is the main ore mineral for lead. Because of its relatively low melting temperature, it can be easily smelted and has been used as a source of lead since ancient times. Galena has a cubic crystal system and can often be found as cubes or octahedra. Its shiny grey metallic luster and heavy, dense nature make it easy to identify. Galena often contains small amounts of silver, which add to its economic value.
Pyrite is a common iron sulphide mineral found in many different geological settings. It has a brassy-yellow metallic colour that has caused many people to mistake it for gold, giving it the name “Fool’s gold”. Pyrite and gold can be quite easily distinguished from one another: pyrite is less yellow and much lighter and harder than gold, which can be scratched with a pocket knife. Pyrite often forms perfect cubes, which can grow to quite large sizes, because of its crystal structure. The word pyrite comes from the Greek word ‘pyr’ meaning fire, because it will spark if hit with other metal or stone objects.
Quartz is the second most abundant mineral on Earth, occurring in many different types of rocks. Although usually clear or milky white in colour, quartz can be found in a variety of colours because of impurities in the crystal structure. Pure quartz is made up of silicon and oxygen only, but atoms of other elements, like iron or titanium, often make their way into the quartz crystal structure. Some varieties of quartz, like purple amethyst, are considered to be semi-precious gemstones and have been used since ancient times to make jewellery and decorative objects.
Rhodochrosite is a manganese carbonate mineral that is usually bright pink or red in colour. Other elements like iron, magnesium or calcium can substitute for manganese, giving the mineral a more grey, yellow or brown colour. Rhodochrosite takes its name from Ancient Greek “rhodochros”, meaning rose-coloured. Because of its distinct colour, it is rarely confused with other minerals. Rhodochrosite usually forms in metamorphic and sedimentary rocks, precipitating out of chemical solutions circulating through the rock. When precipitation occurs in several separate episodes, different layers form, each with a slightly different composition and colour, giving it a banded appearance. Rhodochrosite is mainly used in jewellery and is often found and mined from silver deposits. Well-developed rhombic crystals are very rare.
Sphalerite is the main ore mineral for zinc, and although relatively common, finding it in commercial amounts is somewhat rarer. The zinc will give the mineral a yellow or red hue, but iron can replace the zinc in the atomic structure, making the crystals black. Rarely, cobalt finds its way into the structure, and produces green crystals. Although sphalerite is a relatively soft mineral, it can be cut (faceted) into attractive gems, which are used for mineral displays.
This sample is from the Keystone mine on the west side of the Coldwater River, 6 km north of Coquihalla Lakes in southwestern BC.
The area was first staked in the early 1900s and developed in the 1930s. The mine was only active for a year, producing 81 tonnes of ore in 1955.
The mine’s main ore minerals can be seen in this sample: rhodochrosite, sphalerite and galena with small amounts of chalcopyrite. These occur with barite and quartz in narrow veins up to around 10 cm wide.
At Keystone, the veins are concentrated along a shear zone about 150 m wide, which is an area that has been deformed and faulted. The ore fluids traveled along the shear zone, eventually cooling and precipitating the minerals seen there. The banding seen in the sample suggests several pulses of fluids with slightly different compositions flowed through the rock to form the veins.
Store: Association for Mineral Exploration (AME)
Accession #: AME 506
Primary Mineral: Barite , Galena, Pyrite, Rhodochrosite & Sphalerite
Secondary Mineral: Quartz
Site Locality: Keystone Mine
Location: Coldwater River, Caquihalla Lakes, British Columbia
Special Features: n/a