Metallic Luster Gemstones: Pyrite, Hematite and Marcasite
Metallic Luster Gemstones: Pyrite, Hematite and Marcasite
[For Information and Educational purposes only]
by Alice Koh
Luster refers to the light reflected from a gemstone's surface. Words that describe luster include adamantine (like diamond), vitreous (like glass), silky, resinous, greasy and metallic of which the latter being the most reflective. Gemstones with metallic luster usually have a refractive index ranging from about 2.6 to more than 3.0, which is a bit higher than the refractive index of diamonds, which is 2.4.
Three best known gemstones with metallic luster are pyrite. hematite and marcasite. They are all iron-based minerals that can be used in jewellery. Although, historically the jewelry reported as Marcasite of ancient times was in fact pyrite or a metal with a similar appearance. Even today a gemstone sold as marcasite you can be sure that it is actually pyrite.
In terms of hardness on the Mohs scale, pyrite is 6 to 6.5 which makes it hard to be scratched with a steel penknife. It is harder than other yellow metallic minerals, and its streak is black, usually with a tinge of green. Although pyrite has a reasonably good level of hardness it is quite brittle.
Pyrite occurs in cubic, pentagonal dodecahedra, octahedra crystal structure. Its colours range from gray yellow to brassy yellow which is very similar in appearance to gold. Thus it is also known as Fool's Gold.
Pyrite has a high density of 5.00 - 5.20. It is opaque in transparency and occurs with an indistinct cleavage.
Pyrite is derived from the Greek PUR and LITHOS meaning Fire and Stone or “the stone which strikes fire.” Pyrite has been found in prehistoric burial mounds giving evidence of its early use as a fire starter. Pieces of pyrite have also been used as a spark-producing material in flintlock firearms.
Pyrite or iron pyrite is composed of iron sulfide, sometimes containing small amounts of cobalt, nickel, silver and gold. It is considered the most common form of sulfide minerals. It forms in almost all types of environments: sedimentary, igneous and metamorphic rock types. However, pyrite rarely forms in fresh-water environments.
Not only does its colour resembles gold, pyrite is often formed together with gold. In some deposits pyrite contains enough included gold to warrant mining.
Pyrite has been used since the Stone Age and the ancient civilization created ritual magical objects and jewellery using pyrite. Historically, pyrite was widely used in jewellery, but is rarely seen in jewellery today.
Pyrite is found all over the world and comes in large crystals. However, the most important and largest deposit of pyrite is from Peru.
The perfect cubes of pyrite embedded in a matrix are found in abundance in the Victoria Mine, Navajun and La Rioja Mines in Spain. These are highly esteemed and sought after by collectors.
Pyrite deposits are also found also in Bolivia, Mexico, Sweden, Romania and the USA (Colorado).
Hematite
Both pyrite and hematite are iron-rich minerals. They have similar physical makeup and can be found in many areas of the world. However when discovered in its rawest form, hematite is usually found in shades of red. It turns black upon continuous exposure to wind and rain. Hematite is usually red, dark brown, black or silver. It produces a rust or red-colored streak when scratched.
Hematite is opaque and has an extremely variable appearance. Its luster can range from earthy to submetallic to metallic. Hematite is harder than pure iron but is much more brittle. Its hardness ranges from 5.5 to 6.5 on the Mohs scale. It has no cleavage and it occurs in trigonal, mostly platy crystal structure. Its density is 5.12 to 5.28 which is a bit higher than that of pyrite. (Pyrite has a density of 5.00 - 5.20).
Hematite forms in the shape of rhombohedral crystals and has the same crystal structure as sapphires and rubies.
Hematite comes from the Greek HAIMATITES LITHOS which means "blood-red stone" as it leaves a rust-red streak when scratched in a white ceramic plate. This red streak is an important clue in identifying hematites.
Varieties of hematite include: kidney ore (looks like a kidney), martite, iron rose and specularite (specular hematite). Maghemite (a product of oxidised magnetite) is also loosely called a hematite.
Many specimens of hematite contain enough magnetite that they are attracted to a common magnet. Magnetite is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is important to note that a magnetite leaves a black streak unlike the red streak from hematites.
In ancient Rome, hematite was the material used for signet rings and intaglios. In England, during the Victorian era, hematite was used in jewellery. Many Native American tribes used red ochre, the powdered form of hematite, extensively as a face paint for religious and war-related ceremonies. Note: Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite.
Ancient Egyptians placed hematite amulets, representing pillows, in tombs to help mummies arise and move on to the afterlife. See Chapter CLXVI: The Chapter of the pillow in THE BOOK OF THE DEAD, The Papyrus of Ani. [Note, CLXVI = 166].
Ancient Romans associated hematite with Mars, the god of war whom they glorified. Their warriors rubbed their body with powdered hematite as it was believed it made them invincible.
Hematite has been found on planet Mars. This discovery is significant as terrestrial hematite is typically a mineral formed in watery environments. This points to the fact that there was once water on Mars.
Hematite deposits are found in the UK (Cumberland), Bangladesh, Brazil, China, New Zealand, the Czech Republic and the USA (Minnesota).
Marcasite
Marcasite is similar to pyrite in appearance and physical properties, and it has the same chemical composition. The most distinguishing feature of marcasite is its blade- or needle-shaped crystals and its streak is pure gray as compared to pyrite's slight green. Pyrite and marcasite have been mistaken for gold because they are yellow and metallic.
Marcasite is derived from the Arabic word "markaschatsa," meaning "fire stone." This is because when struck with flint or iron, marcasite can actually spark fire. It is sometimes referred to as "white iron pyrite".
Marcasite is of a grey-black (silver glint) with a black matrix colour. It is opaque in transparency with a poor cleavage. It has a metallic luster when polished. However it tarnishes easily and its luster becomes submetallic and specimens will alter to a brownish colour over time even in a home environment.
Marcasite has a hardness ranging from 6 to 6.5 on the Mohs scale with a specific gravity ranging from 4.8 - 5.2 which is less dense than pyrite. However, marcasite is brittle and chemically unstable. When exposed to moisture or humid environment, it can produce small amounts of sulfuric acid. For these reasons marcasite is never used in jewellery.
In the early 1800s people used the word marcasite for pyrite and other yellow iron sulfide minerals. In 1845 marcasite was classified as an orthorhombic iron sulfide thus differing from pyrite. Pyrite is found everywhere and is a mineral known worldwide whereas marcasite is not as common as pyrite and not known or recognized by people who are enthusiasts and aficionados of rocks.
[For Information and Educational purposes only]
by Alice Koh
Luster refers to the light reflected from a gemstone's surface. Words that describe luster include adamantine (like diamond), vitreous (like glass), silky, resinous, greasy and metallic of which the latter being the most reflective. Gemstones with metallic luster usually have a refractive index ranging from about 2.6 to more than 3.0, which is a bit higher than the refractive index of diamonds, which is 2.4.
Three best known gemstones with metallic luster are pyrite. hematite and marcasite. They are all iron-based minerals that can be used in jewellery. Although, historically the jewelry reported as Marcasite of ancient times was in fact pyrite or a metal with a similar appearance. Even today a gemstone sold as marcasite you can be sure that it is actually pyrite.
In terms of hardness on the Mohs scale, pyrite is 6 to 6.5 which makes it hard to be scratched with a steel penknife. It is harder than other yellow metallic minerals, and its streak is black, usually with a tinge of green. Although pyrite has a reasonably good level of hardness it is quite brittle.
Pyrite occurs in cubic, pentagonal dodecahedra, octahedra crystal structure. Its colours range from gray yellow to brassy yellow which is very similar in appearance to gold. Thus it is also known as Fool's Gold.
Pyrite has a high density of 5.00 - 5.20. It is opaque in transparency and occurs with an indistinct cleavage.
Pyrite is derived from the Greek PUR and LITHOS meaning Fire and Stone or “the stone which strikes fire.” Pyrite has been found in prehistoric burial mounds giving evidence of its early use as a fire starter. Pieces of pyrite have also been used as a spark-producing material in flintlock firearms.
Pyrite or iron pyrite is composed of iron sulfide, sometimes containing small amounts of cobalt, nickel, silver and gold. It is considered the most common form of sulfide minerals. It forms in almost all types of environments: sedimentary, igneous and metamorphic rock types. However, pyrite rarely forms in fresh-water environments.
Not only does its colour resembles gold, pyrite is often formed together with gold. In some deposits pyrite contains enough included gold to warrant mining.
Pyrite has been used since the Stone Age and the ancient civilization created ritual magical objects and jewellery using pyrite. Historically, pyrite was widely used in jewellery, but is rarely seen in jewellery today.
Pyrite is found all over the world and comes in large crystals. However, the most important and largest deposit of pyrite is from Peru.
The perfect cubes of pyrite embedded in a matrix are found in abundance in the Victoria Mine, Navajun and La Rioja Mines in Spain. These are highly esteemed and sought after by collectors.
Pyrite deposits are also found also in Bolivia, Mexico, Sweden, Romania and the USA (Colorado).
Hematite
Both pyrite and hematite are iron-rich minerals. They have similar physical makeup and can be found in many areas of the world. However when discovered in its rawest form, hematite is usually found in shades of red. It turns black upon continuous exposure to wind and rain. Hematite is usually red, dark brown, black or silver. It produces a rust or red-colored streak when scratched.
Hematite is opaque and has an extremely variable appearance. Its luster can range from earthy to submetallic to metallic. Hematite is harder than pure iron but is much more brittle. Its hardness ranges from 5.5 to 6.5 on the Mohs scale. It has no cleavage and it occurs in trigonal, mostly platy crystal structure. Its density is 5.12 to 5.28 which is a bit higher than that of pyrite. (Pyrite has a density of 5.00 - 5.20).
Hematite forms in the shape of rhombohedral crystals and has the same crystal structure as sapphires and rubies.
Hematite comes from the Greek HAIMATITES LITHOS which means "blood-red stone" as it leaves a rust-red streak when scratched in a white ceramic plate. This red streak is an important clue in identifying hematites.
Varieties of hematite include: kidney ore (looks like a kidney), martite, iron rose and specularite (specular hematite). Maghemite (a product of oxidised magnetite) is also loosely called a hematite.
Many specimens of hematite contain enough magnetite that they are attracted to a common magnet. Magnetite is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is important to note that a magnetite leaves a black streak unlike the red streak from hematites.
In ancient Rome, hematite was the material used for signet rings and intaglios. In England, during the Victorian era, hematite was used in jewellery. Many Native American tribes used red ochre, the powdered form of hematite, extensively as a face paint for religious and war-related ceremonies. Note: Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite.
Ancient Egyptians placed hematite amulets, representing pillows, in tombs to help mummies arise and move on to the afterlife. See Chapter CLXVI: The Chapter of the pillow in THE BOOK OF THE DEAD, The Papyrus of Ani. [Note, CLXVI = 166].
Ancient Romans associated hematite with Mars, the god of war whom they glorified. Their warriors rubbed their body with powdered hematite as it was believed it made them invincible.
Hematite has been found on planet Mars. This discovery is significant as terrestrial hematite is typically a mineral formed in watery environments. This points to the fact that there was once water on Mars.
Hematite deposits are found in the UK (Cumberland), Bangladesh, Brazil, China, New Zealand, the Czech Republic and the USA (Minnesota).
Marcasite
Marcasite is similar to pyrite in appearance and physical properties, and it has the same chemical composition. The most distinguishing feature of marcasite is its blade- or needle-shaped crystals and its streak is pure gray as compared to pyrite's slight green. Pyrite and marcasite have been mistaken for gold because they are yellow and metallic.
Marcasite is derived from the Arabic word "markaschatsa," meaning "fire stone." This is because when struck with flint or iron, marcasite can actually spark fire. It is sometimes referred to as "white iron pyrite".
Marcasite is of a grey-black (silver glint) with a black matrix colour. It is opaque in transparency with a poor cleavage. It has a metallic luster when polished. However it tarnishes easily and its luster becomes submetallic and specimens will alter to a brownish colour over time even in a home environment.
Marcasite has a hardness ranging from 6 to 6.5 on the Mohs scale with a specific gravity ranging from 4.8 - 5.2 which is less dense than pyrite. However, marcasite is brittle and chemically unstable. When exposed to moisture or humid environment, it can produce small amounts of sulfuric acid. For these reasons marcasite is never used in jewellery.
In the early 1800s people used the word marcasite for pyrite and other yellow iron sulfide minerals. In 1845 marcasite was classified as an orthorhombic iron sulfide thus differing from pyrite. Pyrite is found everywhere and is a mineral known worldwide whereas marcasite is not as common as pyrite and not known or recognized by people who are enthusiasts and aficionados of rocks.