Volume: 100ml +- 2% (yes, I couldn’t believe it either); Mass: measurement pending, but above 200g

I just bought a mineral identification book and it says to take a streak. I tried with tiles at home, but I am not sure which scratches which. If I don’t apply force, I see nothing. With enough force, I see very little white powder on the tile and white marks on the stone. I am not sure, whether the tiles are untreated. Here is the tile: enter image description here

Here the stone after streak tests: enter image description here

The stone is also harder than the coins I tried. They leave golden or red streaks on it.

With red streak from 2 cent coin: enter image description here

With golden streaks from 10 cent coin: enter image description here

The stone was given to me near Lafkos, 37006, Greece and probably found on a nearby beach, hence the rounded shape.

From the pictures in my book, I might guess green apatite, but I doubt it has the required density (book says between 3.16 and 3.22g/cm^3 I now try to determine weight and volume, but I have to ask my neighbours, because it exceeds the 200g limit of my precision scale.

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    $\begingroup$ The streak test result can be described as "no streak", which happens with hard minerals. The white powder is from the tile being powdered by the harder stone. Do you have a piece of quartz that you can use to see if it can be scratched easily by the quartz? $\endgroup$ – haresfur Jul 16 '18 at 5:22
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    $\begingroup$ Yes Ludi any Quartz has practicaly the same hardness. we ask for that because if A mineral has 5 of hardness, if it scratches B mineral, B mineral is less from 5 at mohos hardness scale and delimitates what the mineral can be. Quartz can have different colors because of impurities but all of them have the same crystalographic structure and very close hardness. $\endgroup$ – user12525 Jul 16 '18 at 16:07
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    $\begingroup$ @Universal_learner thank you for your guidance. I ordered it. It was said to arrive before Jul 30. I hope it does, because I have some fights planned for later. I have been pestering my neighbours for a kitchen scale, but vainly so far. Sooner or later we will know the density. $\endgroup$ – Ludi Jul 16 '18 at 17:05