The Mineral apophyllite
Apophyllite can be a beautiful mineral, forming in lustrous, transparent crystals that are well-formed and occasionally very large. Though it is found worldwide in volcanic zeolite environments, the Indian traprock quarries have produced enormous quantities of this mineral in all different shapes, sizes, and colors, making Apophyllite easily obtainable and very affordable.
Apophyllite was originally regarded as a single mineral, with a variable ratio of fluorine to hydroxyl. In 1978, the IMA sub-classified into two distinct minerals: Fluorapophyllite and Hydroxyapophyllite. In 1981, an additional rare member with sodium replacing the potassium was added to the group, and called Natroapophyllite.
In a controversial move, the IMA has recently changed the scientific naming of these minerals for easier cataloging and alphabetical indexing. The new mineral names are Apophyllite-(KF) [instead of Fluorapophyllite], Apophyllite-(KOH) [instead of Hydroxyapophyllite], and Apophyllite-(NaF) [instead of Natroapophyllite]. Although use of the original names is now discouraged by the IMA, these names are still used and referenced, with the new names frowned upon by many collectors. The reality is that most collectors rarely sub-classify Apophyllite specimens, and simply label them all as Apophyllite.
Apophyllite-(KF) is the most common and abundant of the group. Most specimens labelled simply as "Apophyllite" are of the Apophyllite-(KF) form. Apophyllite-(KOH) is less common, but is still the dominating form of Apophyllite in several localities, including most of the Virginia occurrences. Apophyllite-(NaF) is very rare, and is found sparingly at only a few localities.
Apophyllite almost always occurs together with zeolites, especially in traprock environments. Apophyllite appears very similar to the zeolites, and is sometimes even confused with them. However, the physical structure of Apophyllite is different, with tetrahedrons aligning in sheets as a phyllosilicates, as opposed to the zeolites which are tectosilicates.
Carletonite is a rare blue mineral that is similar to Apophyllite, and it only occurs in Mont Saint Hilaire, Quebec, Canada. Many classify Carletonite as group member within the Apophyllite group.
Apophyllite is named from a combination of the Greek word "apo" - to be off, and "phyllos" - leaf, alluding to the property of this mineral that it exfoliates (flakes apart like a leaf) when heated due to loss of water in its structure.
Apophyllite-KF: KCa4Si8O20(F,OH) · 8(H2O)
Apophyllite-KOH: KCa4Si8O20(OH,F) · 8(H2O)
Apophyllite-NaF: NaCa4Si8O20F · 8(H2O)
Colorless, white, gray, green, brown. Rarely pink, purple, red, or orange.
Crystals are most often in cubic-shaped crystals, with distinctive triangular corners. Commonly in perfect, pseudocubic or rectangular crystals, as well as sharply pointed prismatic pyramidal crystals that are usually doubly terminated. Also tabular, blocky, in cubic groups, in platy clusters, druzy, and in stalactitic formations of crystals. An unusual habit is in blocky radiating sprays and rounded groupings resembling disco balls. Crystals are almost always striated.
(Note: Apophyllite-(KF) and Apophyllite-(KOH) both crystallize in the tetragonal crystal system, whereas Apophyllite-(NaF) crystallizes in the orthorhombic system.)
Hydrous calcium potassium fluoro-hydroxyl-silicate. The ratio fluorine to hyroxyl varies among two group members, and the potassium is replaced with sodium in another member.
Crystal habits and mode of occurrence.
Mostly in volcanic rock, within basalt and in seams in diabase. Also in low temperature metamorphic veins in gneiss and in cavities in pegmatite dikes.
Apophyllite can form in large and very-well formed crystals, which are of interest to collectors. Colored crystals of Apophyllite such as green and red are highly desired by collectors.
Apophyllite is common worldwide in many basalt and diabase quarries, though large, well-formed crystals are limited to several important localities. By far, the largest crystals are from the Deccan Traprocks of India, and can be found in abundance in the zeolite-producing basalt quarries there. Important Indian localities include Pune (Poona), Jalgaon, Nasik, and Mumbai (Bombay). Some of the best green Indian Apophyllites, with a deep emerald-green color, came from the Pashan Quarries in the Pune District. Exquisite clusters of"Disco ball" shaped aggregates have come from well diggings in Momon Akhada, Rahuri, India.
A classic locality that produced highly-desirable pink Apophyllite crystals is St. Andreasberg, Harz Mountains, Lower Saxony, Germany. In Africa, good crystals of Apophyllite-(KOH) come from the Wessels Mine and N'Chwaning Mines in the Kalahari Manganese Fields of South Africa.
In the U.S., New Jersey has produced the best Apophyllite in several important localities. The Upper New
Street Quarry, Paterson; and nearby Prospect Park, both in Passaic Co., are known for their exceptional well-formed crystals, usually white in color. Equally important is the Millington Quarry, Somerset Co., which has produced crystals and platy aggregates with outstanding luster. Very good Apophyllite crystal plates and drusy
forms were also extracted in the diabase
seams of Laurel Hill (Snake Hill), Secaucus; and Bergen Hill, both in Hudson Co.
Exceptional Apophyllite of the (KOH) type have come from the Fairfax Quarry, Centreville, Fairfax Co., Virginia. Druzy
microcrystals associated with blue Kinoite have come from the Christmas Mine, Gila Co., Arizona.
Distingushing Similar Minerals
Chabazite- Has rhombohedral crystal angles and lack crystal modifications, crystals not
striated like Apophyllite.
Heulandite - Different crystal form.
Calcite - Different crystal form, has lower hardness.