If you are fascinated by the hidden structures of our planet, you have likely come across
PENFIELDITE. 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
PENFIELDITE. 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,
PENFIELDITE is defined by the chemical formula
Pb2Cl3(OH).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.
PENFIELDITE crystallizes in the
Hexagonal 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
Trigonal dipyramidal.
- Point Group: 6
- Space Group: P6
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
PENFIELDITE, the dimensions of this microscopic building block are:
a=11.39Å, c=4.02Å, Z=3
The internal arrangement of these atoms is described as:
Halides are ionically bonded compounds of cations Na1+, Ca2+, etc. & halogen anions F1-, Cl1-, Br1-, I1-; oxyhalides, hydroxyhalides & related double halides with Pb (As, Sb, Bi, etc.) w/o Cu; Pb[3+3+2] biccaped trig prisms share edges & corners to form hexagonal framework with channels // [0001]; stereochemistry of Pb2+ is commonly influenced by lone-electron-pair effect, whereby electron pair on ion effectively prevents bonding in that direction with result that near neighbors of Pb2+ are all on 1 side of ion.1 All atoms lie on symmetry planes at either z = 0 or z = ½; 2 independent Pb atoms, Pb1 & Pb2, are linked to 8 anions in bicapped trig prismatic configuration; 2 coorinations do not match btw each other, in fact Pb1 is surrounded by 6 Cl + 2(OH), whereas Pb2 is surrounded by 7 Cl + 1(OH); bases of Pb1-centered prisms are almost prf equilateral triangles, those of Pb2-centered prisms are severly distorted triangles; positions of coordinating anions around Pb reveals that they can be divided in 2 pairs, Cl3 & (OH), & Cl1 & Cl2, which play balanced xl-chemical roles in Pb1- & Pb2- centered polyhedra.2This 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
PENFIELDITE in the field, what does it actually look like? A mineral’s “habit” describes its typical shape and growth pattern.
- Common Habit: Prismatic macro crystals or steeply pyramidal; parallel groups
- Twinning: About [2130] on {0001} and on {4154}, both contact twins
Twinning is a fascinating phenomenon where two or more crystals grow interlocked in a specific symmetrical pattern. If PENFIELDITE 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 oxidized hydrothermal Pb-deposit; seawater action on slagKnowing 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.
PENFIELDITE is often related to other species, either through similar chemistry or structure.
Relationship Data:Understanding 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 PENFIELDITE?The standard chemical formula for PENFIELDITE is
Pb2Cl3(OH). This defines its elemental composition.
2. Which crystal system does PENFIELDITE belong to?PENFIELDITE crystallizes in the
Hexagonal system. Its internal symmetry is further classified under the Trigonal dipyramidal class.
3. How is PENFIELDITE typically found in nature?The “habit” or typical appearance of PENFIELDITE is described as
Prismatic macro crystals or steeply pyramidal; parallel groups. This refers to the shape the crystals take when they grow without obstruction.
4. In what geological environments does PENFIELDITE form?PENFIELDITE is typically found in environments described as:
In oxidized hydrothermal Pb-deposit; seawater action on slag. This gives clues to the geological history of the area where it is discovered.
5. Are there other minerals related to PENFIELDITE?Yes, it is often associated with or related to other minerals such as:
.
External Resources for Further Study
For those looking to dive deeper into the specific mineralogical data of
PENFIELDITE, we recommend checking high-authority databases:
Final Thoughts
PENFIELDITE 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
Pb2Cl3(OH) and a structure defined by the
Hexagonal 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.
