Tilasite is a calcium magnesium fluorine arsenate mineral, closely related to adelite. A microprobe analysis by [Dunn] yielded CaO 26.11, MgO 18.84, As2O5 51.51, F 6.85, less O = F 2.88, total = 100.43 wt. %
Tilasite was reported from Sterling Hill by Parker (1978); it is not known from Franklin.
Tilasite occurs as 4 nun, euhedral, milky white crystals with a slightly pearly luster. It fluoresces with a whitish-yellow color in shortwave ultraviolet. No physical or optical data exist.
Tilasite occurs as crystals on a reddish-brown seam of friedelite, associated with barite and calcite in red-willemite ore, and as a milky white coating mixed with white willemite on red-willemite/franklinite ore at Sterling Hill. (Dunn, 1995)

 Location Found: Ogdensburg
 Year Discovered: 1895
 Formula: CaMg(AsO4)F
 Essential Elements: Arsenic, Calcium, Fluorine, Magnesium, Oxygen
 All Elements in Formula: Arsenic, Calcium, Fluorine, Magnesium, Oxygen
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Fluorescent Mineral Properties

 Shortwave UV light: Fairly weak pale yellow, very rare
 Mid wave UV light: Yellow-orange weaker than longwave
 Longwave UV light: Yellow-orange moderate brightness
 To find out more about this mineral at minDat's website, follow this link   Tilasite

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.683

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 58, No. 1 - Spring 2017, pg. 19Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 2, Richard C. Bostwick - Tilasite
View IssueV. 57, No. 1 - Spring 2016, pg. 13Tilasite From Sterling Mine, Ogdensburg, New Jersey: A Newly Recognized Assemblage, James Van Fleet and Earl R. Verbeek, PhD (Long article)
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Tilasite (Fluorescent Info)
View IssueV. 20, No. 1 - March 1979, pg. 7New Minerals - Tilasite
View IssueV. 17, No. 2 - September 1976, pg. 4New Minerals - Bassanite/Tilasite (small article)
No Images at this time.


All content including, but not limited to, mineral images, maps, graphics, and text on the Franklin-Ogdensburg Mineralogical Society, Inc. (FOMS) website is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Creative Commons License