If you are fascinated by the hidden structures of our planet, you have likely come across
JOHILLERITE. This mineral is a compelling subject for study, offering a unique glimpse into the complex chemistry that shapes the Earth’s crust.Whether you are a student identifying a hand sample, a researcher looking for crystallographic data, or a collector curious about a new find, this guide breaks down everything you need to know about
JOHILLERITE. From its precise chemical formula to the geological environments where it thrives, let’s explore what makes this mineral distinct.
The Chemistry Behind the Crystal
Every mineral tells a story through its chemistry. At its core,
JOHILLERITE is defined by the chemical formula
NaMg3Cu(AsO4)3.This isn’t just a string of letters and numbers; it represents the precise recipe of elements that nature used to build this specimen. This specific chemical composition is what gives the mineral its stability and dictates how it reacts with acids, heat, or other minerals. It is the fundamental “DNA” that geologists use to classify it within the larger mineral kingdom.
Crystallography: Geometry in Nature
One of the most beautiful aspects of mineralogy is the hidden geometry within every stone.
JOHILLERITE crystallizes in the
Monoclinic system.Think of this as the mineral’s architectural blueprint. It dictates the symmetry and the angles at which the crystal faces grow. Digging deeper into its symmetry, it falls under the
Prismatic.
- Point Group: 2/m
- Space Group: C2/c
Why does this matter? These crystallographic details are like a fingerprint. They influence optical properties—how light travels through the crystal—and physical traits like how it breaks or cleaves when struck.
Internal Structure and Unit Cell
If we could zoom in to the atomic level, we would see the “Unit Cell”—the smallest repeating box of atoms that builds up the entire crystal. For
JOHILLERITE, the dimensions of this microscopic building block are:
a=11.87Å, b=12.76Å, c=6.77Å, ß=113.4o, Z=4
The internal arrangement of these atoms is described as:
Phosphates, arsenates, vanadates: anions [PO4]3-, [AsO4]3-, [VO4]3- are usually insular; cations may be small with [4] coordination, medium-sized with [6] coordination, or large with [8] or higher coordination; medium-sized cations with octahedral [6] coordination may be insular, corner-, edge- or face-sharing & form major structural units with medium-sized & large cations; stepped chains of edge-sharing octahedra M32+ // [101] share corners with PO4 or AsO4 tetrahedra to give pleated sheets // (010); chains of M[8] polyhedra // [001] interlink sheets.2 □-planar-coordinated site, A(1)’, fully occupied by Cu2+, displaced ¼ along x; A(2) site is similar to other alluaudite-grp minerals, surrounded by 8 O-atoms with = 2.70 Å, & occupied by Na (also other large cations); refined site-scattering values & observed distances of M(1) & M(2) sites in accord occupancy primarily by Mg with Cu2+ at M(1) & Cu2++Fe3++Al at M(2); similar compositions of AsO4 minerals aresniopleite & caryinite; Cu2+ has repl Ca in formula of johillerite.3 Forms continuous solid-solution system with badalovite & nickenichite & discontinuous solid solution with bradaczekite.4This internal structure is the invisible framework that supports everything we see on the outside, from the mineral’s density to its hardness.
Physical Appearance (Habit)
When you find
JOHILLERITE in the field, what does it actually look like? A mineral’s “habit” describes its typical shape and growth pattern.
- Common Habit: Massive
- Twinning:
Twinning is a fascinating phenomenon where two or more crystals grow interlocked in a specific symmetrical pattern. If JOHILLERITE exhibits twinning, it can be a dead giveaway for identification, distinguishing it from look-alike minerals.
Where is it Found? (Geologic Occurrence)
Minerals are the products of their environment. They don’t just appear anywhere; they need specific conditions—pressure, temperature, and chemical ingredients—to form.
Geologic Occurrence:
In complex granite pegmatites; in phosphatic nodules in shaleKnowing this context helps geologists reconstruct the history of a rock formation. It tells us whether the rock was born from cooling magma, settled in an ancient ocean, or was transformed by the intense heat and pressure of metamorphism. For more broad geological context, resources like the
U.S. Geological Survey (USGS) provide excellent maps and data.
Related Minerals
No mineral exists in a vacuum.
JOHILLERITE is often related to other species, either through similar chemistry or structure.
Relationship Data:
Alluaudite groupUnderstanding these relationships is key. It helps us see the “family tree” of the mineral world, showing how different elements can substitute for one another to create an entirely new species with similar properties.
Frequently Asked Questions (FAQs)
1. What is the chemical formula of JOHILLERITE?The standard chemical formula for JOHILLERITE is
NaMg3Cu(AsO4)3. This defines its elemental composition.
2. Which crystal system does JOHILLERITE belong to?JOHILLERITE crystallizes in the
Monoclinic system. Its internal symmetry is further classified under the Prismatic class.
3. How is JOHILLERITE typically found in nature?The “habit” or typical appearance of JOHILLERITE is described as
Massive. This refers to the shape the crystals take when they grow without obstruction.
4. In what geological environments does JOHILLERITE form?JOHILLERITE is typically found in environments described as:
In complex granite pegmatites; in phosphatic nodules in shale. This gives clues to the geological history of the area where it is discovered.
5. Are there other minerals related to JOHILLERITE?Yes, it is often associated with or related to other minerals such as:
Alluaudite group.
External Resources for Further Study
For those looking to dive deeper into the specific mineralogical data of
JOHILLERITE, we recommend checking high-authority databases:
Final Thoughts
JOHILLERITE is more than just a name on a list; it is a testament to the orderly and beautiful laws of nature. With a chemical backbone of
NaMg3Cu(AsO4)3 and a structure defined by the
Monoclinic system, it holds a specific and important place in the study of mineralogy.We hope this overview has helped clarify the essential data points for this specimen. Whether for academic study or personal interest, understanding these properties brings us one step closer to understanding the Earth itself.
