SUPPORT US. Covid-19 has significantly affected our fundraising. Please help!
Log InRegister
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsBooks & Magazines
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsMineral Shows & EventsThe Mindat DirectoryDevice Settings
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryMineral Photography

Identity HelpFound near Eels Lake, Ontario, Canada. Is this Actinolite or Fluorapatite?

5th Aug 2020 00:48 BSTCeyea Spooks

Brand new to the rock hounding world. My late uncle was big into it in the 70's around our family cottage on Eels Lake.

I found this right on the shoreline of the lake, at the mouth of an old Uranium exploration site. I believe this to be Actinolite or Fluorapatite, but I was hoping to get some other opinions! 


5th Aug 2020 01:07 BSTEd Clopton Expert

Welcome to Mindat!

Thanks for providing a decent photo and precise locality information.  (Lots of folks will just say either "Ontario", which doesn't narrow it down very well, or nothing but "Eels Lake" without specifying even what continent it's on!)  How large is it?  It's helpful either to state dimensions or to include something familiar (pencil point, hand, pop can, hammer, automobile) in the photo for scale.

Both apatite and actinolite can be this color, and both have similar hardness (apatite is the standard for hardness = 5 on the Mohs scale; actinolite is between 5 and 6), but their crystal forms are different.  Ideally apatite will have a hexagonal cross-section like a pencil, whereas actinolite should have a diamond-shaped or skewed rectangular cross-section.  Both also can be kind of rounded without showing a clear shape.  Apatite is often, though not always, fluorescent in ultraviolet light; actinolite probably isn't since it often contains a little iron, which kills any fluorescence.

I'm guessing actinolite, since it's a little tougher and more chemically resistant than apatite and thus more likely to survive, but either one is possible.

5th Aug 2020 01:38 BSTHolger Hartmaier

Hi Ceyea,
It looks like actinolite-tremolite to me. I am familiar with this area and there are several localities where this type of material can be found. Check out the rock cuts at the Dyno Road turnoff from Highway 28. This locality is described in Mindat. Here is a photo of material from there.

That is a nice sample by the way!

5th Aug 2020 02:11 BSTPaul Brandes Manager

Welcome to Mindat, Ceyea!

Beautiful specimen, and thank you for providing at least a little information to go with it. I would tend to agree with actinolite. A check with a UV light would be a great first check to see if it's fluorescent, for the reasons Ed mentioned. However, sometimes the only way to tell them apart is by analytical analysis.

5th Aug 2020 02:58 BSTFrank K. Mazdab Manager

break off one of the crystals from the back of the specimen (where it won't mar the appearance) and smash it... actinolite will have well-developed classic 56°/124° amphibole cleavage (or maybe it'll break a little splintery), whereas apatite will just break into irregular fragments... there might be a weak cleavage perpendicular to the long axis of the crystal, but chances are you'll mostly get fracturing.

Then take one of the very small fragments you just broke and put it in a cup of hydrochloric acid: apatite will disappear after sitting overnight in dilute hydrochloric acid, whereas actinolite will still be there to greet you in the morning.

5th Aug 2020 05:04 BSTHerwig Pelckmans Expert

Frank K. Mazdab Manager  ✉️

actinolite will still be there to greet you in the morning.
Great description of some easy tests. I just love the quote above! :-)
Thanks for making me smile in the morning!

Cheers, Herwig
ACAM & MKA (Belgium)

5th Aug 2020 14:26 BSTAndrew Debnam

Hello Ceyea, as others have said this is most likely Actinolite-Tremolite series (an Amphibole)  When the  roads were expanded in the vicinity of Eels Lake in the 1970's and early 1980's some exposures were found.  The exact position of them is lost. As Holger pointed  a similar exposure was created further north of Eels Lake at Dyno Rd and HWY 28. It was blasted again last summer and some fresh material was found.  Follow Franks advice on cleavage to confirm Amphibole. Fluorapatite from the area does not look like this and exhibits parting or flat breakage at a right angle to "length" of the crystal.  Fluorapatite in from the Bancroft area does not fluoresce.  Much of the so called Actinolite from the area has turned out to be Tremolite as an aside.  

5th Aug 2020 16:29 BSTDonald B Peck Expert

I tried to insert a section of a magnified screen shot here from Ceyea's photo but it wouldn't let me (or I don't know what I am doing).  At about 8 o'clock and halfway from the center to the edge  in the photo, there is a small fragment, apparently below the crystal from which it came,  that fragment has a distinctly hexagonal shape.  Also some of the longer blue crystals seem to exhibit parting planes (or am I seeing things that are not there?)  I am leaning towards apatite.

5th Aug 2020 17:23 BSTRichard Gunter Expert

The sample looks very similar to several of the tremolite localities in the Bancroft area. They used to be called actinolite when all green amphibole was actinolite and all black amphibole was hornblende but even the deep green Ca clinoamphiboles are now tremolite. There is a large area of calcareous metasediment in the Anstruther Township/Chandos Township region that was mapped by D.M. Shaw in 1962 and most of this will have tremolite.

6th Aug 2020 23:53 BSTCeyea Spooks


Wow, thanks everyone for the overwhelming input! What a welcome to this wonderful site. In the future I will be sure to include something in the photo as a scale reference. This piece is 53.80 ct and is approximately 1 cubic inch in size.

I am looking forward to trying the HCl test this weekend. The consensus seems to be Apatite or an Actinolite-Tremolite series, so this test should provide some good insight.

I attempted to fracture a few pieces but was unable to make any further determination based on the cleavage or lack thereof.

Here is another macro shot at 4x magnification.


6th Aug 2020 23:54 BSTCeyea Spooks

And one more, also at 4X

7th Aug 2020 09:12 BSTHerwig Pelckmans Expert

Hi Ceyea,

From the general appearance of the crystals on the specimen, My best guess would also be the actinolite-tremolite series.
Please do let us know what the tests will reveal this weekend. :-)

Cheers, Herwig
ACAM & MKA (Belgium)
Mineral and/or Locality is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization. Public Relations by Blytheweigh.
Copyright © and the Hudson Institute of Mineralogy 1993-2020, except where stated. Most political location boundaries are © OpenStreetMap contributors. relies on the contributions of thousands of members and supporters.
Privacy Policy - Terms & Conditions - Contact Us Current server date and time: September 24, 2020 12:43:29
Go to top of page