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Lava Cave Minerals and Films

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Lava caves host diverse secondary minerals deposited by seeping, mineral-rich water. Common formations include gypsum crystals and flowers, calcite speleothems (stalactites, stalagmites, flowstone), and colourful opal varieties. Bacterial biofilms, often appearing as white or colored coatings, are found within a small number of caves within Auckland.

Initial analysis has identified some of the mineral deposits within Auckland's Lava Caves, however a significant portion remains unidentified. The composition of these unknown minerals is currently speculative and requires further investigation. Future research and analysis are anticipated to shed light on the nature and properties of these mineral formations. Where possible, hypothesised mineral identifications have been provided for the observed  deposits.

Bacterial Biofilms

Bacterial biofilms are communities of bacteria that live together, surrounded by a slimy substance they produce themselves. In lava caves, these biofilms often colonise rock surfaces, walls, and ceilings and can come in a wide array of colors, textures, and morphologies. The microbial composition of these biofilms can vary depending on factors such as the cave’s geochemistry, nutrient availability, and environmental conditions.

The northern section of Mira cave is adorned with a magnificent bright white biofilm that shimmers and sparkles, resembling a constellation of tiny stars. This breathtaking display is considered one of the most exquisite features of Auckland’s lava caves and was only discovered in 2023. The biofilm, possessing a unique soapy texture, is intricately patterned with millions of minute squiggles.

 

Encrustations & Speleothems

Encrustations, in the context of lava caves, are mineral deposits that form on the surfaces of cave walls, ceilings, and floors. These deposits can occur through various processes, such as the evaporation of mineral-rich water, the precipitation of minerals from dripping water, or the deposition of minerals by microorganisms. Encrustations can vary in composition, texture, and appearance, ranging from thin, translucent films to thicker, more robust layers. Common minerals found in lava cave encrustations include gypsum, calcite, opal, and various iron oxides.

Speleothems, a specific type of encrustation, are formed by the deposition of minerals from dripping or flowing water. In lava caves, speleothems are typically composed of minerals such as calcite, aragonite, and gypsum. These formations can take on a variety of forms, including stalactites, stalagmites, and flowstone. The growth and morphology of speleothems are influenced by factors such as the rate of water flow, the mineral content of the water, and the temperature and humidity within the cave.

  

 

  

 

 

 

Crystal formations

Crystal formations are less common than in limestone caves and often form as secondary mineral deposits, precipitated from mineral-rich water seeping through the porous lava rock. While the specific types of crystals vary depending on the geological composition of the lava and the surrounding environment, some common examples include gypsum, calcite, and various types of opal. Gypsum crystals can manifest as delicate, flower-like clusters as well as tabular formations.

 

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  7. Lava Cave Minerals and…