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Hemimorphite

earth science Maturity 7-9 Next article →

Hemimorphite is a significant silicate mineral with the chemical formula Zn4(Si2O7)(OH)2·H2O. It is a primary component of the mineral calamine. This mineral matters because it serves as an important ore of zinc. An ore is a mineral source used to extract metals. Hemimorphite contains up to 54.2% zinc by weight. It also consists of silicon, oxygen, and hydrogen.

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The formation of hemimorphite follows a specific geological process. It most frequently occurs through the oxidation of certain ore bodies. These ore bodies contain a mineral called sphalerite. As these upper parts of the ore oxidize, hemimorphite forms. This process usually happens alongside other secondary minerals. These minerals together create a structure known as a gossan. A gossan is often called an iron cap.

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Hemimorphite-227534

Hemimorphite displays several distinct physical forms. It can appear as massive crystalline crusts or flat layers. Sometimes it forms granular or rounded aggregates. These aggregates can show concentric striations, which are small grooves. Other specimens appear as fine, needle-shaped, or fibrous structures. It can also grow in stalactitic shapes. In rare cases, the crystals form fan-shaped clusters.

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The name of the mineral comes from its unique crystal growth. This is known as hemimorph development. This term describes crystals that are terminated by dissimilar faces. This means the two ends of the crystal look different. One end of the crystal is typically blunt. The opposite end is typically sharp. This type of development is typical of only a few minerals.

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History shows that scientists once misunderstood this mineral. In the past, hemimorphite and smithsonite were both called calamine. Smithsonite is a zinc carbonate with the formula ZnCO3. Because they look so much alike, people thought they were the same. This changed during the second half of the 18th century. Researchers discovered that calamine actually contained two different compounds. Hemimorphite was identified as the rarer silicate of the two.

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Hemimorphite-278499

Many different regions around the world contain hemimorphite deposits. In the United States, it is found in several states. These include Montana, Colorado, and New Mexico. It is also found in Pennsylvania and the Missouri lead-zinc district. International deposits are also quite common. You can find it in China and Mexico. It appears in Italy, Austria, and England. It is also found in Thailand and North Africa. Even Siberia and Sardinia have deposits.

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Hemimorphite-227534

One of the most interesting properties of hemimorphite is fluorescence. This is when a mineral glows under ultraviolet light. The color of the glow depends on the light used. If you use shortwave ultraviolet light at 253.7 nm, it shows strong green fluorescence. If you use longwave UV light, it shows a weak light pink fluorescence. This makes the mineral very striking to observe in a lab.

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Hemimorphite-227534
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