Septarian Nodule (Yellow Jasper variety)

Physical Properties

Hardness: 3.5-4 (for calcite) to 6.5-7 (for the jasper/chert matrix). Color: Tan, yellow, or gold matrix with dark brown or grey patterns. Luster: Dull to waxy. Crystal structure: Trigonal/Orthorhombic components. Often shows 'lightning' or 'turtle' patterns.

Formation & Geological History

Formed during the Cretaceous period (50-70 million years ago) specifically through the dehydration of clay-rich mud balls on ancient sea floors, which cracked and were later filled with minerals like calcite and aragonite.

Uses & Applications

Primarily used for decorative purposes, lapidary arts, jewelry (cabochons), and as museum or collector pieces. Some are sliced to reveal the inner 'star' patterns.

Geological Facts

Also known as 'Dragon Stones' due to their scaly, cracked appearance. The name comes from the Latin 'septum,' meaning a partition or wall, referring to the cracks that divide the stone.

Field Identification & Locations

Identify in the field by looking for rounded, heavy nodules that often have distinct angular cracks or 'veins' on the surface. Commonly found in Utah, USA and Madagascar. Look for the contrast between the yellow/tan matrix and dark inner veins.

Identified on: 4/13/2026

Mode: Standard