Earth Record
Mineralogy and formation
Atlantisite is a trade name for a natural intergrowth, usually green serpentine hosting purple stichtite, and its geology is a lesson in alteration followed by overprinting. The serpentine portion begins in ultramafic rock, rich in olivine and pyroxene, that has reacted with water during serpentinization. That process hydrates and restructures the original mantle derived minerals into softer sheet silicates and related phases.
Stichtite arrives later, typically where chromium from chromite or chromium bearing host minerals becomes mobilized and combines with magnesium, carbonate, hydroxyl, and water. The purple veins are therefore not ornamental accidents. They are the second chapter.
Formation begins with ultramafic parent rocks such as peridotite or dunite. Low temperature hydrothermal alteration introduces water and often carbon bearing fluids, transforming the rock into serpentine rich masses. If chromium is present and local fluid chemistry supports carbonate hydroxide formation, stichtite can crystallize in seams and pockets. Tasmania is famous because that sequence is so well expressed there.
The specimen preserves a fluid mediated conversation between a hydrated magnesium silicate host and a later chromium bearing layered double hydroxide mineral.
There is no single crystal system for atlantisite because it is not one mineral. Serpentine group members vary, while stichtite is trigonal. Structurally that matters. The green host and purple vein material obey different crystallographic rules, and the specimen's power comes from retaining those distinctions instead of homogenizing them. One part records hydration of ultramafic rock. The other records chromium rich late stage mineral growth in fractures and altered zones. It is an intergrowth of processes, not a compromise phase halfway between them.
That is why the material feels collaborative rather than blended. Serpentinization is one of geology's great acts of softening, converting harsh ultramafic assemblages into hydrated, lower temperature architectures. Stichtite adds an unexpected color and a later mineral logic without erasing the earlier one. The final bodily note follows the petrology itself: balance here is not achieved by flattening contrast but by allowing two distinct mineral histories, one earthier and one more delicate, to remain in contact long enough that the rock learns to carry both at once.
The specimen keeps that dialogue visible in real mineral terms, hydration beside later chromium enrichment, suggesting that equilibrium sometimes begins when two unlike structures stop trying to cancel each other.
Stichtite: Trigonal (Rhombohedral), Space Group R-3M structure
Chemical FormulaStichtite: Mg6Cr2(OH)16CO3 . 4H2OCrystal SystemStichtite: Trigonal (Rhombohedral), Space Group R-3MMohs Hardness1.5Specific Gravity2.1-2.2 (stichtite) / 2.5-2.6 (serpentine)-composite ~2.3-2.5LusterWaxy to pearly (stichtite), waxy to greasy (serpentine)ColorGreen-PurpleIMA StatusrockIMA NumberNone (trade name for serpentinite variety; Stichtite component is pre-IMA 1910) Type locality (for the trade name): Stichtite Hill, Dundas, western Tasmania, Australia
Type locality (for stichtite mineral): Dundas, Tasmania (described 1910)
Barberton, South Africa (serpentinite-hosted stichtite)
Great Dyke, Zimbabwe
Various ophiolite complexes worldwide (where chromite-bearing serpentinites weather)
Atlantisite forms through the serpentinization of ultramafic rocks (peridotites) that contain chromite. Serpentinization is a major hydrothermal process in which olivine and pyroxene, the primary minerals of mantle peridotite, react with water to produce serpentine-group minerals, brucite, and magnetite. The basic reaction for olivine serpentinization is: 6(Mg,Fe)2SiO4 + 7H2O = 3(Mg,Fe)3Si2O5(OH)4 + Fe3O4 + H2 (Okamoto et al.
, 2024; Sabuda et al. , 2021; Nascimento Vieira et al. , 2020). This process typically occurs at temperatures below 400 degrees C and produces highly alkaline fluids with pH values reaching 11 or higher. The stichtite component forms when chromium is released during the weathering and alteration of chromite (FeCr2O4), a common accessory mineral in ultramafic rocks. As chromite weathers under alkaline, carbonate-rich conditions produced by serpentinization, Cr3+ is liberated and combines with Mg2+, CO3^2-, OH-, and water to crystallize stichtite in the interstices of the serpentine matrix.
The co-occurrence of stichtite and serpentine is therefore a direct consequence of chromite-bearing peridotite undergoing serpentinization in the presence of CO2-bearing fluids. Chromium mobility in serpentine soils has been studied extensively, showing that Cr is gradually exposed by weathering of parent materials and that chemical modification of chromite increases near the soil surface (Cheng et al.
, 2011; Davaasuren et al. , 2024). The type locality for this combination is Stichtite Hill at Dundas, Tasmania, Australia, where Precambrian ultramafic rocks have undergone extensive serpentinization. The geological setting is an ophiolite complex, a fragment of ancient oceanic crust and upper mantle that was obducted onto continental crust. Similar assemblages occur in other ophiolite/serpentinite terranes worldwide, but the Tasmanian material is prized for its vivid color contrast and large stichtite patches (Pereira & Peinado, 2012; Huang et al.
, 2023).
Tasmania (Australia)
Telling it apart
Atlantisite is not a mineral species, it is a rock made of purple stichtite and green serpentine, and the main confusion is sellers presenting it as one rare crystal. The key distinction is mixed hardness and obvious two material structure: the purple stichtite is extremely soft, about Mohs 1. 5 to 2, while the green serpentine is harder, roughly 2. 5 to 4. A single needle or point dragged across different color zones will not behave the same.
Genuine atlantisite shows blotchy to veined purple patches inside green serpentine, usually opaque and waxy rather than glassy. Dyed composites often have unnaturally sharp purple boundaries or color concentrated in pits. Lepidolite and serpentine mixes can look similar at a glance, but lepidolite shows micaceous sparkle and a different feel. Because atlantisite is a trade name, ask for the actual components.
If the seller cannot say stichtite plus serpentine, they are selling a story, not an identification. The fraud risk is real because trade names hide what the holder is really buying, and a mixed rock should not be priced like a rare single species crystal.
Spotting the real thing
Atlantisite is a natural intergrowth of green serpentine and purple stichtite. Both should be present. Specific gravity approximately 2.
3-2. 5. Waxy to pearly luster.
If only one color is present, it is not atlantisite. Genuine specimens come almost exclusively from Tasmania, Australia. Check for natural intergrowth; the purple and green should merge organically, not look painted or glued.
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