Apophyllite is a beautiful mineral, frequently forming in lustrous, transparent crystals that are occasionally very large. Though it is found worldwide in volcanic zeolite environments, the Indian traprock quarries have produced large quantities of this mineral in all different shapes, sizes, and colors, making Apophyllite easily obtainable and very affordable.
Nomenclature of Apophyllite
The name Apophyllite now refers to a specific group of phyllo-silicate minerals. Apophyllite was originally regarded as a single mineral, with a variable ratio of fluorine to hydroxyl (OH). The IMA (International Mineralogical Association) made changes to the nomenclature system used for this group in 1978, 1981, 2008 and 2013. The frequency of changes to the nomenclature system has created much confusion. The minerals currently included in the Apophyllite Group are: Fluorapophyllite-(K), Fluorapophyllite-(Na), Fluorapophyllite-(Cs), Fluorapophyllite-(NH₄), Hydroxyapophyllite-(K), and Hydroxymcglassonite-(K). The distinctions among the different names are virtually impossible to detect with the naked eye.
Fluorapophyllite-(K) is the most common and widespread member of the group, and it is usually the species considered when “apophyllite” is used as a general name. 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.
Occurrence and Appearance
Apophyllite almost always occurs together with zeolites, typically as secondary minerals in basalt or other volcanic rocks. The mineral 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 phyllo-silicates, as opposed to the zeolites which are tectosilicates. Apophyllite also occurs in low temperature metamorphic veins in gneiss and in cavities in pegmatite dikes.
Crystals are most often in cubic-shaped crystals, with distinctive triangular corners. Commonly found in perfect, pseudo-cubic or rectangular crystals, as well as sharply pointed prismatic pyramidal crystals that are usually doubly terminated. Also found as tabular, blocky crystals, 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.
Color is usually colorless or white but also can be green, brown, gray, pink, purple, red, or orange. Apophyllite crystals with colors such as green and red are highly desired by collectors.
In general, the Apophyllite minerals belong to the Tetragonal Crystal System. However, Fluorapophyllite-(Na) crystallizes in the Orthorhombic system. Hardness is 4 – 5 on the Mohs scale. Luster is vitreous to pearly. Apophyllite may occasionally fluoresce yellow or white.
Apophyllite is common worldwide in many basalt and diabase quarries, but 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, Jalgaon, Nasik, and Mumbai. 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 Hydroxyapophyllite-(K) come from the Wessels Mine and N’Chwaning Mines in the Kalahari Manganese Fields of South Africa. Other worldwide localities include Mont Saint-Hilaire in Canada, as well as Kongsberg, Norway, and Scotland, Ireland, Brazil, and Japan.
In the United States, New Jersey has produced the best Apophyllite in several important localities. The Upper New Street Quarry, Paterson; and nearby Prospect Park, both in Passaic County, are known for their exceptional well-formed crystals, usually white in color. Equally important is the Millington Quarry, Somerset County, which has produced crystals and platy aggregates with outstanding luster. Very good Apophyllite crystal plates and druzy forms were also extracted in the diabase seams of Laurel Hill (Snake Hill), Secaucus; and Bergen Hill, both in Hudson County, New Jersey.
Exceptional Hydroxyapophyllite-(K) have come from the Fairfax Quarry, Centreville, Fairfax County, Virginia. Druzy microcrystals of Apophyllite associated with blue Kinoite have come from the Christmas Mine, Gila Co., Arizona.
Article by Bill Jones, Sidewinder Minerals