Mineral of the Month: Apatite
by Bob Farrar
The Mineral of the Month for April is apatite, or, more properly, the “apatite group,” as “apatite” is not one mineral but a group of related minerals. These minerals often occur as well-developed crystals, they are frequently colorful, and they can make beautiful gemstones, all of which make them popular with collectors.
“Apatite” is a group of phosphate minerals, presently including dozens of species. The most familiar species contain calcium, phosphate groups, and either fluorine, chlorine, or hydroxyl groups, and are properly known as “fluorapatite”, “chlorapatite”, and “hydroxylapatite”, respectively. Confusingly, these names were changed to “apatite-(CaF),” “apatite-(CaCl),” and “apatite-(CaOH)”, respectively, in 2008, for various reasons, including to make them fall together when listed in alphabetical order. Wishing to be correct, many collectors spent hours making new labels for their specimens. Then, much to everyone’s consternation, the names were changed back to fluorapatite, chlorapatite, and hydroxylapatite in 2010.
Members of the apatite group crystalize in the hexagonal system, but a dizzying array of crystal habits, or variations of hexagons, are known. For example, instead of having six sides, a crystal might have twelve sides. Crystals sometimes resemble beryl, but are much softer, with a hardness of 5 on the Mohs scale. Other physical properties include an inconspicuous basal and prism cleavage, specific gravity of 3.1 to 3.2, and a glassy luster. A wide range of colors are known, including blue, purple, green, red, yellow, brown, and white.
Of the three species listed above, fluorapatite is by far the most common. In common usage, fluorapatite is often referred to simply as “apatite”. If you hear someone speak of “apatite,” chances are that it’s fluorapatite.
The most important occurrences for the apatite group, at least from a collector’s viewpoint, are in pegmatites. Fluorapatite is often deposited late in the formation of pegmatites. In such cases, the apatite crystals can be found on top of cleavelandite, quartz, mica, and other minerals lining pegmatite pockets. Among the finest of this type are purple crystals of fluorapatite found at the Pulsifer Quarry, located at the aptly named Mt. Apatite in Maine. Mt. Apatite and other localities in Maine are still producing fluorapatite specimens. Numerous pegmatites in Brazil, Pakistan, Afghanistan, South Dakota, and other localities have produced fine fluorapatite specimens. Good crystal specimens of hydroxlapatite are not common, but beautiful green crystals up to a few centimeters across were found at the Sapo Mine in Minas Gerais, Brazil almost 20 years ago.
Fluorapatite occurs in numerous environments in addition to pegmatites. In Morocco, yellow to green crystals are found in ultrabasic rocks. Transparent yellowish-green crystals are found in a magnetite deposit at Cerro de Mercado, Mexico. In Ontario, very large (up to 300 kg.) brown to green crystals of apatite are found embedded in calcite. It is common in ore vein deposits, such as at Panasqueira, Portugal, as well as in Germany, England, and the Czech Republic. Alpine fissure deposits, such as in Switzerland, Italy, and Austria also produce fluorapatite.
Maryland is not without fluorapatite, though perhaps not so spectacular as that from some other areas. It occurs in some of the pegmatites in Maryland, such as the Ben Murphy Mica Mine. Blebs of blue apatite an inch across were found in calcite at the Greenspring Quarry in Baltimore. Small greenish crystals were found at the Delight Quarry in Baltimore Co. Fluorapatite is also found at a number of the Northern Virginia traprock quarries.
Fluorapatite, when transparent, can be facetted into beautiful gemstones. Blue and purple materials make particularly nice stones. “Neon blue” apatite, found in Madagascar, when faceted, can resemble some of the neon blue Paraiba tourmalines, but costs a small fraction as much. Fibrous material can be cut into cabochons that show cat’s eyes.
The apatite group of minerals includes a wide variety of species, crystal habits, and colors. Even for collectors who might specialize in these minerals, there are always going to be more different forms to seek out. Some are rare and valuable, but others are common enough that just about any collector can add them to their collection.
by Bob Farrar
The Mineral of the Month for April is apatite, or, more properly, the “apatite group,” as “apatite” is not one mineral but a group of related minerals. These minerals often occur as well-developed crystals, they are frequently colorful, and they can make beautiful gemstones, all of which make them popular with collectors.
“Apatite” is a group of phosphate minerals, presently including dozens of species. The most familiar species contain calcium, phosphate groups, and either fluorine, chlorine, or hydroxyl groups, and are properly known as “fluorapatite”, “chlorapatite”, and “hydroxylapatite”, respectively. Confusingly, these names were changed to “apatite-(CaF),” “apatite-(CaCl),” and “apatite-(CaOH)”, respectively, in 2008, for various reasons, including to make them fall together when listed in alphabetical order. Wishing to be correct, many collectors spent hours making new labels for their specimens. Then, much to everyone’s consternation, the names were changed back to fluorapatite, chlorapatite, and hydroxylapatite in 2010.
Members of the apatite group crystalize in the hexagonal system, but a dizzying array of crystal habits, or variations of hexagons, are known. For example, instead of having six sides, a crystal might have twelve sides. Crystals sometimes resemble beryl, but are much softer, with a hardness of 5 on the Mohs scale. Other physical properties include an inconspicuous basal and prism cleavage, specific gravity of 3.1 to 3.2, and a glassy luster. A wide range of colors are known, including blue, purple, green, red, yellow, brown, and white.
Of the three species listed above, fluorapatite is by far the most common. In common usage, fluorapatite is often referred to simply as “apatite”. If you hear someone speak of “apatite,” chances are that it’s fluorapatite.
The most important occurrences for the apatite group, at least from a collector’s viewpoint, are in pegmatites. Fluorapatite is often deposited late in the formation of pegmatites. In such cases, the apatite crystals can be found on top of cleavelandite, quartz, mica, and other minerals lining pegmatite pockets. Among the finest of this type are purple crystals of fluorapatite found at the Pulsifer Quarry, located at the aptly named Mt. Apatite in Maine. Mt. Apatite and other localities in Maine are still producing fluorapatite specimens. Numerous pegmatites in Brazil, Pakistan, Afghanistan, South Dakota, and other localities have produced fine fluorapatite specimens. Good crystal specimens of hydroxlapatite are not common, but beautiful green crystals up to a few centimeters across were found at the Sapo Mine in Minas Gerais, Brazil almost 20 years ago.
Fluorapatite occurs in numerous environments in addition to pegmatites. In Morocco, yellow to green crystals are found in ultrabasic rocks. Transparent yellowish-green crystals are found in a magnetite deposit at Cerro de Mercado, Mexico. In Ontario, very large (up to 300 kg.) brown to green crystals of apatite are found embedded in calcite. It is common in ore vein deposits, such as at Panasqueira, Portugal, as well as in Germany, England, and the Czech Republic. Alpine fissure deposits, such as in Switzerland, Italy, and Austria also produce fluorapatite.
Maryland is not without fluorapatite, though perhaps not so spectacular as that from some other areas. It occurs in some of the pegmatites in Maryland, such as the Ben Murphy Mica Mine. Blebs of blue apatite an inch across were found in calcite at the Greenspring Quarry in Baltimore. Small greenish crystals were found at the Delight Quarry in Baltimore Co. Fluorapatite is also found at a number of the Northern Virginia traprock quarries.
Fluorapatite, when transparent, can be facetted into beautiful gemstones. Blue and purple materials make particularly nice stones. “Neon blue” apatite, found in Madagascar, when faceted, can resemble some of the neon blue Paraiba tourmalines, but costs a small fraction as much. Fibrous material can be cut into cabochons that show cat’s eyes.
The apatite group of minerals includes a wide variety of species, crystal habits, and colors. Even for collectors who might specialize in these minerals, there are always going to be more different forms to seek out. Some are rare and valuable, but others are common enough that just about any collector can add them to their collection.
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Hydroxylapatite on Feldspar,
Sapo Mine, Minas Gerais, Brazil. Bob Farrar photo and specimen. |
Fluorapatite,
Imilchil, Morocco. Bob Farrar photo and specimen. |