THE GEMSTONE LIBRARY
Shattuckite — Milpillas, Mexico
Blue copper silicate specimens from Milpillas, Sonora, with locality history, crystal textures and advice for caring for delicate surfaces.
About this page: A material profile with our collection image and published mineralogical context. Sources describe their own researched specimens; this profile is not a laboratory report for every pictured piece.
Our Milpillas collection
Our January 2025 photograph shows an assortment of bright blue shattuckite specimens supplied as material from Milpillas, Mexico. These are mineral specimens whose interest lies in their natural surface textures as well as their colour. Unlike a single faceted jewel, a specimen can contain several growth areas, remaining host rock and associated minerals. The appearance may change as it is turned, with the light catching raised clusters and softer-looking blue surfaces. The collection’s stated locality is important, but the photograph does not identify a particular mining level or discovery pocket. Published accounts of Milpillas material provide geological and collecting context; they are not a claim that our pieces came from the exact discoveries described in those accounts.
The mineral behind the blue
Shattuckite is a copper silicate with the formula Cu₅(SiO₃)₄(OH)₂. It belongs to the orthorhombic crystal system and commonly occurs as aggregates of slender, needlelike crystals rather than large, transparent crystals suitable for conventional faceting. These aggregates can produce a silky appearance or form rounded clusters. The mineral is named after the Shattuck mine at Bisbee, Arizona, its type locality. Its blue colour and copper chemistry place it within a fascinating family of secondary minerals formed as copper-bearing rocks change near the surface. Shattuckite is not the same mineral as chrysocolla, even though the two may occur together and both can contribute blue or blue-green areas to a specimen.
Milpillas and documented discoveries
Milpillas lies near Cuitaca in Sonora, northern Mexico. A Mineralogical Record field report describes a January 2019 discovery at the mine’s 1100 level. In that account, deep blue shattuckite first appeared as felted inclusions within colourless quartz; a later generation formed sky-blue, rounded coatings on matrix, associated with pale green chrysocolla. This is a useful example of how a mineral can take more than one form even within a single locality. “Botryoidal” means a surface resembling a cluster of grapes, while “acicular” describes needlelike crystals. Those terms help explain specimen shapes without suggesting that every blue area has identical chemistry. The published discovery date belongs to that documented find, not to all shattuckite offered under the Milpillas name.
How this kind of specimen forms
Shattuckite is associated with the oxidised zones of copper deposits, where pre-existing minerals react with water and oxygen and copper can be redistributed. Silica and the local chemical environment help determine which secondary minerals develop. A specimen therefore records a sequence of changes rather than a single moment of formation. Quartz, chrysocolla, malachite and other minerals may accompany shattuckite, depending on the locality and the particular growth environment. Colour alone cannot reliably separate all of these materials. Where exact identification matters, examination or analysis is more informative than matching a specimen to a photograph. Our page uses the supplied collection identification and explains the mineral generally; it does not present a new laboratory determination of every constituent in the pictured assortment.
What to look for
View a specimen first as a whole, then study the edges of the blue growth. Does the surface consist of tiny rounded mounds, fibrous patches or more angular structures? Are there clear crystals over the blue material, or exposed areas of host rock? Soft side lighting often reveals relief better than direct frontal light. A magnifier can help show why a surface appears silky, but avoid pressing the lens against the specimen. Photographing the same piece from several angles provides a useful record of fragile edges and associated minerals. A locality label should stay with the specimen, particularly if it is later moved between display cases or passed to another collector.
Care and personal meaning
Shattuckite is comparatively soft, around Mohs 3½, and fine crystal aggregates can be easily damaged. Handle specimens by a stable part of their matrix rather than rubbing the blue growth. Avoid scrubbing, abrasive polishing, chemical cleaners and ultrasonic cleaning. For delicate specimens, careful dry dusting with a very soft brush is usually a better starting point than soaking; seek advice if the matrix or associated minerals are unstable. Keep pieces in padded individual compartments during transport. Some collectors associate blue minerals with calm or communication as a personal practice. That interpretation can sit alongside an appreciation of the mineral’s geology, but it is not evidence of a therapeutic effect.