Septarian

Septarian is a concretion rather than a single mineral, a nodule of sedimentary rock whose internal cracks have been filled by calcite and aragonite (CaCO₃) veins. Septarian nodules formed 50-70 million years ago when volcanic activity killed marine life, which sank to the seafloor and decomposed. The decomposition produced chemical reactions in the surrounding sediment that caused mud to compact into hard, ball-shaped concretions. As the concretions dried, they contracted and cracked internally, creating the characteristic angular crack patterns.

Over time, mineral-rich groundwater percolated through these internal cracks, depositing golden calcite crystals in the fissures and brown aragonite along the crack walls. The result is a three-part stone: gray limestone/mudstone exterior, brown aragonite crack walls, and bright yellow calcite crystal fills. When cut and polished, the contrast between these three components creates the distinctive dragon-scale or turtle-shell pattern.

The name 'septarian' comes from the Latin 'septum' meaning partition - referring to the internal walls that divide the nodule into chambers. The Moeraki Boulders on New Zealand's South Island coast are giant septarian concretions up to 2 meters in diameter, eroding from coastal cliffs.

Septarian is immediately recognizable when cut - the angular pattern of yellow calcite veins in brown aragonite within gray mudstone creates a unique appearance no other stone replicates. The calcite veins may contain visible crystal terminations.

Distinguish from dragon blood jasper (green and red, completely different composition), turtle jasper (marketing name for various patterned stones), and artificial resin-filled stones. Genuine septarian's calcite veins respond to acid (fizzing confirms carbonate).