Magnesiochromite is very similar to Chromite , and is often mistaken for it. Due to t... More
Magnesiochromite is very similar to Chromite, and is often mistaken for it. Due to their similarity, it is very difficult to visually distinguish these two minerals. Magnesiochromite is the magnesium-dominating form in a series with Chromite, whereas Chromite is iron-dominating. Hide
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The most common form of Magnesite is white, microcrystalline , porous masses that are... More
The most common form of Magnesite is white, microcrystalline, porous masses that are dull in luster, and have the appearance of unglazed porcelain. Because they are porous, they adhere to the tongue when licked. An interesting Magnesite occurrence is in Brumado, Brazil, where a deposit of clear, well formed, rhombohedrons similar to Iceland Spar Calcite found. Until this find, such crystals were, although identical in appearance to Iceland Spar Calcite, they are much rarer and sought after. Common Iceland Spar Calcite has been wrongly labeled by some unscrupulous dealers as Magnesite to stimulate sales.
Magnesite belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a solid solution series. All members of the calcite group crystallize in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction in transparent rhombohedrons. Hide
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Magnetite is best known for its property of being strongly attracted to magnet s. Som... More
Magnetite is best known for its property of being strongly attracted to magnets. Some forms of Magnetite from specific localities are in fact themselves magnets. Commonly known as Lodestone, this magnetic form of Magnetite is the only mineral that is a natural magnet. Due to the magnetism of Lodestone, small iron particles are often found clinging to its surfaces. (Some dealers may even intentionally place metallic filings on a Lodestone to demonstrate its magnetism.) Magnetite may form a yellow-brown rust coating if washed or kept in a moist area. If a specimen is washed, it should be dried to prevent rusting. Rust can easily be removed by soaking the Magnetite in a rust-removing solvent such as Iron Out. The mineral Hematite is known to form pseudomorphs over Magnetite. Such pseudomorphs are commonly known as Martite, and their appearance may be very similar to regular Magnetite. However, they differ from Magnetite in that they are only weakly attracted to magnetic fields, and have a reddish-brown streak. Hide
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Malachite is a popular mineral with its intense green color and beautiful banded mass... More
Malachite is a popular mineral with its intense green color and beautiful banded masses. The banded specimens are formed by massive, botryoidal, reniform, and especially stalactitic Malachite that are dense intergrowths of tiny, fibrous needles. Dense banded specimens are often sliced and polished to bring out their beautiful coloring. The bands may consist of concentric rings with interesting patterns; such specimens are highly sought after. These concentric banded specimens are most commonly from African sources. Polished, banded Malachite has been carved into ornaments and worn as jewelry for thousands of years, and in some ancient civilizations it was thought to be a protection from evil when worn as jewelry. Malachite is generally found together with blue Azurite, and sometimes the two may occur admixed or banded together, forming what is commonly known in the gem and mineral trade as " Azure-Malachite". Malachite may also replace Azurite crystals, retaining the original Azurite shape but chemically altering it.
For additional information, see the gemstone section on Malachite. Hide
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div Manganite is a mineral named for its dominating manganese content. It forms in ma... More
Manganite is a mineral named for its dominating manganese content. It forms in manganese deposits, where it is more common than perceived as an uninteresting mineral. However, several localities produce very aesthetic, well-crystallized forms of Manganite that are highly lustrous. These exceptional examples, especially those from Ilfied in Germany, are rarities that are highly prized by collectors, with high-end collectors vying for the top specimens of this mineral. Hide
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Manganoneptunite is the manganese dominant variant of Neptunite , having a greater po... More
Manganoneptunite is the manganese-dominant variant of Neptunite, having a greater portion of manganese over iron in a solid solution series. Although often considered a variety of Neptunite, the IMA recognizes Manganoneptunite as a distinct mineral species. Manganoneptunite is generally ligher in color than Neptunite, and can even be completely transparent in specimens where the iron content is very low. Hide
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Marcasite is the lesser known companion of the famous mineral Pyrite . Marcasite has ... More
Marcasite is the lesser known companion of the famous mineral Pyrite. Marcasite has the same chemical formula as Pyrite, but crystallizes in a different crystal system, thereby making it a scientifically distinct mineral species. Aggregates of iron sulfide (FeS 2) where the crystal structure cannot be determined without complex analysis may be wrongly labeled by dealers and collectors. Some Marcasite specimens are labeled as Pyrite, and some Pyrite specimens as Marcasite. Pyrite used as a gemstone is also improperly termed in the jewelry trade as Marcasite. This is wholly incorrect, as Marcasite is not used as a gemstone. Marcasite is the most prevalent mineral to experience a condition known as pyrite decay, in which a specimen will slowly disintegrate into a white powder. Little is known about this detrimental condition. It only effects certain specimens at random, while other specimens remain unaffected. However, certain localities are more prone to this condition than others. When a specimen goes through pyrite decay, the sulfur atoms free themselves and form an acid powder that attacks other sulfide minerals and mineral labels. It is most important to remove an afflicted specimen from other minerals, to prevent this condition from spreading. Hide
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Marialite is the sodium rich end member of the Scapolite series . It is very similar ... More
Marialite is the sodium-rich end member of the Scapolite
series. It is very similar and often indistinguishable from
Meionite, the other end member of the series. Intermediary
forms of Marialite and Meionite are frequent, and these are classified
simply as Scapolite. Marialite is named after Maria Rosa von Rath, the wife of German mineralogist Gerhard von Rath (1830-1888). Hide
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Meionite is the calcium rich end member of the Scapolite series . It is very similar ... More
Meionite is the calcium-rich end member of the Scapolite series. It is very similar and often indistinguishable from Marialite, the other end member of the series. Intermediary forms of Meionite and Marialite are frequent, and these are classified simply as Scapolite. Of the two Scapolite minerals, Meionite is the more prevalent form. Meionite is named for the Greek word meion (μειον), which translates as "minus", in reference to its lesser termination angles when compared to Vesuvianite. Hide
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Melanophlogite is a rare form of silica , and is in a unique class in that it contain... More
Melanophlogite is a rare form of silica, and is in a unique class in that it contains organic compounds in its chemical structure. This technically excludes it from being classified as a mineral, since one of the definitions of a mineral is that it is an inorganic substance. Despite this, the acclaimed Dana's System of Mineralogy categorizes Melanophlogite and a few other rare organic 'minerals' together with the true minerals, being that it is naturally formed and irrelevant of biological interference. In a few deposits, such as the Case Montanini Quarry in Italy, the Melanophlogite has been pseudomorphed into Quartz or Opal. Hide
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Mercury is rare in a native state. Although it is a naturally occurring liquid substa... More
Mercury is rare in a native state. Although it is a naturally occurring liquid substance, it is never found in "pools". It only occurs as very small blobs on top of mercury ores such as Cinnabar. The tiny blobs are lodged in small crevices or pores, or just stick to the host mineral. The blobs do not roll around or fall off, but stay attached in position unless tampered with. Mercury freezes at -38º F (-39º C), and when it solidifies, it crystallizes in the isometric crystal system. (Under high pressure it crystallizes in the tetragonal crystal system.) Mercury boils at a very low temperature, and disappears as fumes when heated. Because Mercury is a liquid, it is not possible for it to have the properties of streak, hardness, cleavage, or crystals. Hide
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Mesolite is a fragile member of the zeolite group , and forms almost exclusively in d... More
Mesolite is a fragile member of the zeolite group, and forms almost exclusively in delicate, needle-like crystal habits. It is closely related to Natrolite and
Scolecite, and can appear very similar to them. Chemical analysis or
optical tests are sometimes required to distinguish Mesolite from Natrolite and Scolecite, and a single
crystal may even contain part of each mineral within different zones of the
same crystal. Mesolite is a very brittle and is easy
broken, so care should be exercised when handling specimens. Mesolite is named after the Greek term "Mesos", which means "middle", and "Lithos" - stone. It is named so because Mesolite is intermediary in a series between Natrolite and Scolecite. Hide
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Metacinnabar is an uncommon polymorph of the mineral Cinnabar , forming in a differen... More
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Metavariscite is a rare polymorphous form of the mineral Variscite , and is essential... More
Metavariscite is a rare polymorphous form of the mineral Variscite, and is essentially the same except that its crystal structure differs. It can occur together with Variscite in the same locality, and is very similar in appearance. Hide
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div Miargyrite is an uncommon silver sulfosalt . Though opaque and with a metallic lu... More
Miargyrite is an uncommon silver sulfosalt. Though opaque and with a metallic luster, it may have slight translucent overtones of dark red, especially when containing arsenic in its structure which can replace some of the antimony. Arsenic is responsible for lightening up the color, and when the arsenic fully replaces the antimony, the mineral is no longer Miargyrite, but Smithite, a rare sulfosalt with a bright red color and transparency. Miargyrite is named after the Greek word Meion - "less", and Argyros - "silver", since it contains a lesser percentage silver than other silver ores such as Pyrargyrite.
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Microcline is polymorphous with Orthoclase and Sanidine . These three minerals form t... More
Microcline is polymorphous with Orthoclase and Sanidine. These three minerals form the Potassium Feldspar group. They are almost identical in physical properties, and sometimes it is impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system. Crystals of Microcline are generally much larger than those of
Orthoclase, and a deep green color is tell-tale sign of Microcline, since
Orthoclase does not exist in a deep green color. In some mineral reference guides, Microcline and Sanidine are wrongly
categorized as variety of Orthoclase. Since it is so difficult to
distinguish between Orthoclase, Sanidine, and Microcline, they may be
simply called " Potassium Feldspar". Microcline sometimes forms in association with Albite or other Plagioclase feldspar in alternating patterns, and forms a feldspar rock known as Perthite. Hide
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div Millerite is known for its interesting crystal habit of slender brassy crystal gr... More
Millerite is known for its interesting crystal habit of slender brassy crystal growths and hair-like tufts. It frequently forms inside geodes and vugs where it has the room to develop its interesting crystals. Millerite was named in honor of William Hallowes Miller (1801 – 1880), a prominent Welsh mineralogist responsible for laying the foundations of modern crystallography. The miller indices relating to crystallography are named after him.
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Mimetite is a member of the Apatite group , a group of isomorphous hexagonal minerals... More
Mimetite is a member of the Apatite group, a group of isomorphous hexagonal minerals. It is very similar in structure and appearance to Pyromorphite, and may be partially replaced by it. In fact, sometimes Mimetite and Pyromorphite are virtually indistinguishable from each other and may be wrongly labeled as the other. Mimetite is also structurally similar to Vanadinite, and may also be partially replaced by it. The intermediary member between Mimetite and Vanadinite is known as Endlichite. Hide
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Molybdenite is the most prevalent molybdenum bearing mineral, and is named after that... More
Molybdenite is the most prevalent molybdenum-bearing mineral, and is named after that element. Prior to the discovery of molybdenum as a separate element in 1778 by Karl Wilhelm Scheele, Molybdenite was thought to be Graphite or a lead ore. In fact, the word molybdos means "lead" in ancient Greek. Molybdenite forms in two distinct crystal polytypes: Molybdenite-2H and Molybdenite-3R. Most Molybdenite is of the 2H type, although it is difficult to distinguish the two without complex analysis, and a distinction is rarely made. Molybdenite occurs in lustrous, metallic-looking crystals that can be easily moved and bent out of shape. It also has perfect cleavage in one direction and is often flaky, allowing thin crystals to be "peeled" similar to the micas. Hide
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div Monazite describes a group of several closely related phosphates with a varying r... More
Monazite describes a group of several closely related phosphates with a varying range of several rare earth elements. Due to the similarity and indistinguishable visual differences of the members, a distinction between the Monazite types are rarely designated, with specimens simply labelled as Monazite. Monazite-(Ce), the cerium-rich end member, is by far the most common group mineral of this series, and accounts for most of the known specimens and occurrences.
Monazite is radioactive, and specimens may be metamict with rounded crystal faces. It is named for the Greek work "monazein", meaning alone, alluding to isolated crystals of the original occurrences of this mineral.
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Muscovite is the most common form of mica . Its name is derived from Muscovy Glass , ... More
Muscovite is the most common form of mica. Its name is derived from "Muscovy Glass", which describes thick sheets of transparent mica that were once used as a glass substitute in Russia. Because of Muscovite's abundance, its presence is usually lacking in collections except for it being an accessory mineral to other minerals. However, there are certain interesting formations and colors which are very aesthetic, and those forms are well-represented in collections. Muscovite can come in enormous crystal groupings that can weigh several hundred pounds. Thin sheets can be peeled off as layers, and the thinner a layer is peeled the greater its transparency becomes. Except for large and resistant specimens, Muscovite is very hard to clean because if washed it will absorb water internally and start to break apart. The best way to wash Muscovite and other Micas is with a dry electric toothbrush. Hide
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