ANDRADITE with ACTINOLITE (cabinet)
Andradite is a mineral belonging to the garnet group. Its chemical composition is represented by the formula Ca3Fe2Si3O12.
Andradite has three distinct varieties:
Colophonite: This historical variety is found in the Scandinavian islands and is characterized by a brownish or reddish hue, often appearing opaque or translucent.
Demantoid: Known for its vivid green color, this variety is among the most valuable and rare gemstones in the gemological community.
Melanite: This variety is black due to the limited substitution of titanium for iron and is also referred to as "titanian andradite". It forms a solid solution with morimotoite and schorlomite, depending on the titanium and iron content.
The mineral was first described in 1868 based on a find in Drammen, Buskerud, Norway. It was named in honor of the Brazilian statesman, naturalist, professor, and poet José Bonifácio de Andrada e Silva (1763–1838). Andradite is found in skarns that develop in contact with metamorphosed impure limestones or calcic igneous rocks; it can also be located in chlorite schists, serpentinites, and alkalic igneous rocks (typically titaniferous). Associated minerals include vesuvianite, chlorite, epidote, spinel, calcite, dolomite, and magnetite. This mineral is located in regions such as Iran, Italy, the Ural Mountains in Russia, Arizona, California, and Dnipropetrovsk Oblast in Ukraine.
Actinolite is a silicate mineral belonging to the amphibole group, characterized by the chemical formula Ca2(Mg4.5–2.5Fe2+0.5–2.5)Si8O22(OH)2.
The term actinolite originates from the Greek word aktis (ἀκτίς), which translates to "beam" or "ray", reflecting the fibrous structure of the mineral.
Actinolite serves as an intermediate in a solid-solution series that includes magnesium-rich tremolite, Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2, and iron-rich ferro-actinolite, Ca2(Mg2.5-0.0Fe2+2.5-5.0)Si8O22(OH)2. The crystal structure allows for the free exchange of Mg and Fe ions. Similar to tremolite, asbestiform actinolite is classified as asbestos.
This mineral is typically located in metamorphic rocks, particularly in contact aureoles that form around cooled intrusive igneous rocks. It can also be found as a result of the metamorphism of magnesium-rich limestones.
The historical mineral name uralite is sometimes used to describe an alteration product of primary pyroxene that is largely composed of actinolite. Metamorphosed gabbro or diabase rock formations, known as epidiorite, often contain significant amounts of this uralitic alteration.
Fibrous actinolite is recognized as one of the six types of asbestos, with fibers so fine that they can penetrate the lungs and harm the alveoli. Actinolite asbestos was previously mined along Jones Creek in Gundagai, Australia.
This specimen is from the early '90's from the Kara Mine (Hampshire, Tasmania, Australia) that is not known for any quantity, and it is a rare find.