S-type Cosmic Spherules
S-types are by far the most common cosmic spherules found in Antarctic and rooftop collections. They are mostly composed of silica and have a “chondritic” chemical pattern (meaning they are chemically very similar to chondrites - the most common type of meteorite). They are very texturally diverse and can be split into the following six sub-types…
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Glass spherules (V-types) - These spherules appear as glass drops with a smooth texture and no visible crystals. They often contain vesicles and some contain iron-nickel beads. Their colour varies, but are typically yellow, brown, or clear.
Cryptocrystalline - Cryptocrystalline spherules often have crystals less than a micron in size and a significant amount of magnetite. Some spherules have a "turtle-back" texture with knobbly protrusions of olivines (not shown in this sample).
Barred olivine - This spherule is dominated by parallel grows of olivines arranged in concentric rings with a glassy mesostasis in-between.
Porphyritic olivine (PO) - PO spherules are dominated by olivines within glass and can contain "relict" crystals which are unmelted minerals. They tend to be more vesicular if the crystals are very small, and can have various textures.
Coarse-grained - Spherules with >50% unmelted "relict" crystals are called "coarse-grained". These have experienced the least amount of heating since they still preserve textures and minerals from their precursor meteoroid grain.
CAT spherules - The CAT spherule in this image is the milky white, tear drop-shaped spherule in the centre. The other spherules arranged in a spherical pattern are from various classes and exhibit a diverse range of textures and brown-grey-black colours