Prehnite: meaning, properties and lore

The mineral

Prehnite is a silicate with the chemical formula Ca2Al2Si3O12(OH), and it is described as a basic calcium aluminum silicate, sometimes with some iron. Gemmologists place it among the glassy silicate minerals, a pale green to gray stone that is transparent to translucent. Its hardness is about 6 on the Mohs scale, so it is moderately hard and can be scratched by harder materials.¹²³⁶⁴

Prehnite most often forms rounded, bubbly globular masses made of small saddle-shaped crystals or radiating balls. It commonly lines cavities in igneous rocks and also occurs as stalactite masses. Many specimens are epimorphs that have formed over anhydrite, glauberite and laumontite, which were dissolved away after the prehnite took their shape.³¹²

The colour of prehnite comes from its composition, and it is found in light green, dark green, mint-green, yellowish-green, brownish-green and bluish-green. Rare examples are brown, yellow, orange, pink, gray, white or colorless. Some stones carry a brown ferrous coating that can be removed with chemicals, and in some stones iron content also affects the optical constants and gives chatoyancy.¹³⁶⁵

Prehnite belongs to the orthorhombic crystal system. It has a white streak, a vitreous, waxy or pearly luster, uneven fracture and brittle tenacity. It also shows distinct cleavage in one direction.¹⁵³

Prehnite is a secondary or hydrothermal mineral. It occurs as a low-temperature mineral deposited from ground waters in basaltic rocks, usually alongside zeolites. Its typical settings include basalt and diabase traprock, alpine cavities and metamorphosed gneiss.²⁵¹³

Prehnite is found in the Kayes Region of Mali, which is the most extensive and exploited African source. In the United States the most famous localities are in northwestern New Jersey, including the Upper and Lower New Street Quarries in Paterson. Good material also comes from Kandivali Quarry in Mumbai, India, from Qiaojia and Hongquizhen Quarry in China, and from Prospect and Mullaley in New South Wales, Australia.¹³

Clear specimens of fine colour are sometimes cut for gem use, and prehnite is a highly desired mineral among collectors that is used as a minor gemstone. Gem prehnite is marketed under the name Cape emerald. Australian material has yielded faceted gems up to about 30 carats.²¹⁵

History and lore

The International Gem Society gives the same name origin and adds that Von Prehn first found the material on the Cape of Good Hope. The name therefore links the mineral to the Cape region from which the early European material came.¹⁶⁵

The prehnite from Adams Sound on Baffin Island was collected by Mr. Arthur English as a prospector on the 1910-1911 expedition of the Canadian Government steamer Arctic under Captain J. E. Bernier. A. A. Johnston described it in the Victoria Memorial Museum Bulletin No. 1 in October 1913. The report records a specific gravity of 2.924 at 15.5°C.⁴

Picot de Lapeyrouse named a prehnite variety Koupholite, found in cracks of contact rocks at La Piquette-Dérashids near Barèges in the Pyrenees. Lacroix later identified the mineral in limestone lenses in the Hautes-Pyrénées as prehnite from its optical properties. Lacroix describes the first observation of prehnite as an element of limestone metamorphism as his own contribution, in a note in the Bulletin de la Carte géologique de France (1899-1900).⁷

The Curious Lore of Precious Stones lists New Jersey among the states that are a source of principal gems, and the prehnite of New Jersey is one of the places it names. The same work gives an account of witherite, a barium carbonate, which it says caused spasms of laughter when water it had been dipped in was swallowed.⁸

Professor Pirsson suggested that the high-iron prehnite variety be called ferroprehnite. This proposal was recorded in the Victoria Memorial Museum reports alongside the Baffin Island specimens.⁴

Birthstone and chakra links

Crystal practitioners link prehnite with the Solar Plexus Chakra (yellow) and the Heart Chakra (green), a chakra association that is modern and appears in no older writing.

Prehnite is associated with the zeolites that usually occur with it in basalt, and this mineral association is a fact recorded by Encyclopaedia Britannica. Prehnite is not recorded in the claims as a traditional birthstone or anniversary stone, so no birthstone list or anniversary list is set for it here.²

What crystal practitioners say

Crystal practitioners use prehnite mainly for the mind, and they describe it as a gentle protective stone that supports purification of the personal energy field. Practitioners associate it with enhancing precognition and inner knowing, and advocates say it enables preparation for what is ahead. The stone is sometimes called the prediction stone by practitioners because of its ability to enhance precognitive abilities.

Within crystal healing, prehnite is credited with calming surroundings, fostering peace and offering protection. Practitioners say the stone seals the auric field within a protective shield of divine energy. Harmony with nature and elemental forces is also attributed to it, and practitioners regard it as an excellent stone for contact with nature spirits and the elemental kingdom.

Crystal healing practitioners regard prehnite as a stone of unconditional love and as the crystal to heal the healer. Practitioners also say that placed on the heart or solar plexus during meditation, the stone supports healers. Some practitioners use it as a meditation aid for those who work with others.

Crystal healing traditions associate prehnite with alleviating nightmares, phobias and deep fears, and practitioners say it does this by addressing the root cause. The same traditions associate the stone with supporting dreaming, dream recall and hyperactive children. These are views held within crystal practice and are not recorded as results.

Crystal practitioners recommend cleansing prehnite with running water, moonlight, sage or selenite, and they say salt water should be avoided. Some dealers oil prehnite with lubricants to enhance its luster, a trade practice that practitioners do not endorse. Practitioners attribute their cleansing advice to the stone's softness and to its reaction to salt.³

Crystal healing practitioners say prehnite supports the healing of the lymphatic system, thymus and chest.

What testing has found

Edzard Ernst, who analysed 150 complementary and alternative treatments, found no rigorous trials testing whether crystal healing has therapeutic value. He also wrote that no scientific proof exists for any effect beyond placebo. Pleasant feelings or apparent successes, he suggested, may be explained by the strong placebo effect or by cognitive bias among believers.⁹

Participants holding fake and real crystals reported similar impressions, which suggests a placebo effect could be at play.⁹

Jarry explains that scientists strip interventions of placebo effects in rigorous clinical trials to find any specific benefit.⁹