Jet (lignite) in the context of Gagae

A mineraloid is a naturally occurring substance that resembles a mineral, but does not demonstrate the crystallinity of a mineral. Mineraloid substances possess chemical compositions that vary beyond the generally accepted ranges for specific minerals, for example, obsidian is an amorphous glass and not a true crystal; lignite (jet) is derived from the decay of wood under extreme pressure underground; and opal is a mineraloid substance because of its non-crystalline nature. Pearl is a mineraloid substance because the calcite crystals and the aragonite crystals are bonded by an organic material, and naturally occurs without definite proportions of the components.

The first usage of the term mineraloid substance was in 1909, by mineralogist and geologist Julian Niedzwiedzki, in identifying and describing amorphous substances that resemble minerals.

The Venus of Monruz (also Venus of Neuchâtel, Venus of Neuchâtel-Monruz) is a Venus figurine of the late Upper Paleolithic, or the beginning Epipaleolithic, dating to the end of the Magdalenian, some 11,000 years ago. It is a black jet pendant in the shape of a stylized human body, measuring 18 mm in height. It was discovered in 1991, at the construction of the N5 highway, at Monruz in the municipality of Neuchâtel, Switzerland.

The Venus figurines of Petersfels from a site near Engen, Germany, bear remarkable resemblance to the Venus of Monruz. Especially the biggest of them, called Venus from Engen may have been done by the same artist. It is also made of jet, and also dates to the Magdalenian – to c. 15,000 years ago. The sites of discovery of the two figurines are about 130 km apart.