Sphalerite is a soft stone. With a hardness of only 3.5-4 on the Moh’s scale, it’s normally too soft to be used in jewelry. Moreover, sphalerite’s perfect cleavage in 6 directions means additional care and attention are required for every step of the fashioning process. The specific gravity of 3.9-4.2 puts this mineral in the same range as corundum, and sphalerite is considered to be a relatively dense material.
Sphalerite is a zinc sulfide mineral with a chemical composition of (Zn,Fe)S. It is found in metamorphic, igneous, and sedimentary rocks in many parts of the world. It is the most commonly encountered zinc mineral and the world's most important ore of zinc.
Although sphalerite has been found at a number of localities including; Italy, Switzerland, USA, Namibia, Peru, Mexico, Antarctica, China, Brazil and Canada, the Aliva mine in the Cantabrian Mountains of the northern Spain is the most important locality for it.
The Alina mine is located in Picos de Europa, which are part of the Cantabrian Mountains situated in the North of Spain. This area belongs to the autonomous region of Cantabria. This part of the Picos de Europa is known as the Central massif which includes some 38 peaks of over 2,500 meters in altitude. The mine itself is 1,615 meters above sea level. It can be accessed through a ground track from the village of Espinama (Cantabria) or through the Fuente De cable railway in summer.
The mine was closed in 1989 but before it closed the world’s best and largest transparent stones were extracted from it. Even today nearly all of the newly faceted stones are still derived from the original material. Families of long retired miners may still have some rough and it continues to be slowly released to the market. Clear and good color stones have always been difficult to find and prices have continued to increase as supply dwindles. The material is a challenge to work with not only because of its cleavage but also for its lack of clarity which requires careful orientation to yield the best stones with the least visible inclusions. The colors range from yellow to brown, to green or orange and some pieces are nearly red. The lustre of natural sphalerite is variable and can vary between adamantine to resinous or waxy on some crystal faces. Some stones are zoned and can be fashioned as bi colors. Spectacular pieces can be found in museums and private gem collections around the world. “The Star of Asturias”, at 163.4 cts. is the largest known faceted sphalerite in the world and it is on display at the Cantonal Museum of Geology, in Lausanne, Switzerland.
The deposit is hosted by dolomitic limestones of Carboniferous age but the crystallization of sphalerite itself is thought to have occurred during the Permian age some 250-300 million years ago.
The area is notable for mining and activity has been recorded throughout history. Archaeological remains from between 1500-2000 B.C. reveal that that prehistoric man used the copper minerals from these mountains. However, the Romans were the first to mine the minerals. Although they didn’t have knowledge of zinc, they did manage to produce brass from the copper and zinc sulphide they obtained.