DATA ON THE LIMANU CAVE MINERALOGY, SOUTH DOBROGEA GABRIEL DIACONU*, ŞTEFAN MARINCEA**, DELI DUMITRAŞ** Abstract. By means of diphractometric X-rays analyses on powders, we emphasize an association of minerals in the Limanu Cave from South Dobrogea, made up of hydroxylapatite, brushite, calcite, gypsum and dolomite as the main minerals and quartz and illite as secondary minerals. Key words: cave minerals, Limanu Cave, Dobrogea de Sud. 1. INTRODUCTION The E 95 highway, coming from Bulgaria and linking Vama Veche and Mangalia, crosses the Limanu commune situated close to the Mangalia Lake. A short distance away from the commune, in the right slope of the “La Peşteră” valley, is the entrance of the most important endokarstic void from the entire Dobrogea, namely the Peştera Limanu (Limanu Cave) (Fig. 1). Fig. 1. – Geographic position of the Peştera Limanu (after DUMITRESCU et al., 1965). The labyrinthic cave, with a total length of 3,200 m, was initially shaped naturally as a karstic plateau void, subsequently the cave was influenced by its use in the past as a limestone quarry (the cave humid atmosphere facilitating the mining) as well as a shelter until a much more recent time. The mineralogical samples were collected in places underneath bat colonies which produced the guano deposits on the floor (points 4, 22 and 25) (Fig. 2). Trav. Inst. Spéol. «Émile Racovitza», t. XLVII, p. 65–77, Bucarest, 2008 66 Gabriel Diaconu, Ştefan Marincea, Delia Dumitraş 2 Fig. 2. – Peştera Limanu (partial map after DUMITRESCU et al., 1965; points 4, 22 and 25, sampling sites). The X-rays diphractometric analyses on powders evidenced an association of minerals made up of hydroxylapatite, brushite, calcite, gypsum and dolomite as the main minerals and quartz and illite as secondary minerals. 2. ANALYTIC METHODS From the beginning, we have to point out the micronic-size of the crystals in the analyzed samples. The X-rays diphractometric analyses were made by the powders method. The radiation (Cu, Kα, λ = 1.54056 Å) was monocromatized either by using a graphite monocromator or filtered with Ni. The scanning speed was 0.01º, respectively 0.02º (2θ) per second for 4, respectively 2.4 seconds per step. The parameters of the elemental cells of the mineral species were computed using the refining program by the method of the smallest squares. 3 Data on the Limanu cave mineralogy 67 3. RESULTS AND DISCUSSIONS Hydroxylapatite, [Ca5(PO4)3(OH)], appears as dirty-white, crème or brick- coloured, relatively massive crusts found on the floor covered by clay in a terra rossa facies or on the limestone surface of the walls. Morphologically, the aggregates with a hexagonal habitus suggest an authigenic genesis resulting from precipitation processes. The interreticular distances measured and computed for the main diphractometric reflexes for the two representative hydroxylapatite samples from Peştera Limanu, as well as the Miller indexes established for the hypothesis of the hexagonal symmetry, mineral spatial group P63, are given in Table 1. The average of the two sets of values leads to elemental cells with the size of a = 9.434 (2) Å; c = 6.881 (17) Å and V = 530.4 (11) Å3, the values being very close to those given by BIGI et al. (1996), [a = 9.432 (3) Å; c = 6.881(16) Å]. Table 1 X-rays diphractometric data on powders from two representative samples of hydroxylapatite from Peştera Limanu* Sample PL 6 B Sample PL 10 B Crt. (hkl) no. dmeas.(Å) dcalc. (Å) I / I0 dmeas.(Å) dcalc. (Å) I / I0 1 5.2666 5.2708 4 5.2581 5.2613 3 (101) 2 4.7231 4.7156 2 4.7503 4.7176 3 (110) 3 3.5094 3.5144 1 3.5241 3.5124 3 (201) 4 3.4394 3.4499 42 3.4399 3.4382 72 (002) 5 3.1744 3.1780 1 3.1763 3.1691 7 (102) 6 3.0740 3.0871 11 3.0810 3.0884 14 (210) 7 2.8153 2.8179 79 2.8258 2.8173 100 (211) 8 2.7959 2.7843 100 2.7717 2.7786 82 (112) 9 2.7194 2.7225 33 2.7317 2.7237 35 (300) 10 2.5434 2.5325 12 2.5347 2.5323 9 (301) 11 2.2315 2.2311 12 2.2346 2.2312 36 (221) 12 2.2076 2.2138 1 2.2144 2.2070 2 (103) 13 2.0664 2.0672 12 2.0630 2.0617 6 (113) 14 2.0054 2.0039 16 1.9975 1.9990 21 (203) 15 1.8906 1.8936 19 1.8899 1.8922 9 (132) 16 1.8695 1.8738 7 1.8739 1.8746 23 (230) 17 1.8456 1.8444 20 1.8361 1.8406 19 (213) 18 1.7841 1.7823 5 – – – (410) 19 1.7519 1.7572 29 1.7565 1.7562 25 (402) 20 1.7237 1.7257 11 1.7300 1.7260 5 (141) 68 Gabriel Diaconu, Ştefan Marincea, Delia Dumitraş 4 Sample PL 6 B Sample PL 10 B Crt. (hkl) no. dmeas.(Å) dcalc. (Å) I / I0 dmeas.(Å) dcalc. (Å) I / I0 21 1.7237 1.7250 11 1.7153 1.7191 22 (004) 22 1.6888 1.6877 4 1.6849 1.6823 10 (104) 23 1.6454 1.6466 20 1.6407 1.6459 30 (322) 24 1.6454 1.6464 20 1.6407 1.6439 30 (223) 25 – – – 1.6132 1.6116 32 (313) 26 1.5792 1.5835 2 1.5799 1.5829 6 (412) 27 1.5046 1.5058 11 – – – (124) 28 1.4669 1.4670 1 1.4705 1.4676 7 (510) 29 1.4527 1.4527 2 1.4527 1.4511 5 (323) 30 1.4354 1.4349 20 1.4321 1.4353 7 (511) 31 1.4104 1.4088 16 1.4064 1.4074 7 (143) 32 1.3645 1.3613 13 1.3615 1.3619 24 (600) 33 1.3222 1.3180 21 1.3185 1.3184 18 (431) 34 1.3154 1.3177 26 – – – (404) 35 1.2819 1.2850 22 1.2859 1.2854 24 (521) 36 1.2705 1.2691 9 – – – (234) 37 1.2551 1.2598 16 1.2567 1.2563 26 (215) 38 1.2551 1.2513 16 1.2512 1.2512 9 (342) 39 1.2478 1.2456 9 1.2460 1.2460 27 (610) 40 1.2352 1.2368 21 1.2344 1.2360 36 (513) 41 1.2240 1.2229 20 – – – (252) 42 1.1871 1.1910 7 1.1889 1.1881 21 (225) 43 1.1871 1.1861 7 1.1840 1.1845 8 (504) 44 1.1803 1.1789 7 1.1773 1.1794 5 (440) 45 1.1666 1.1668 6 – – – (350) 46 1.1614 1.1621 12 1.1639 1.1624 3 (441) 47 1.1469 1.1508 32 1.1526 1.1508 28 (351) 48 1.1354 1.1326 16 1.1338 1.1331 8 (260) 49 1.1182 1.1175 10 1.1181 1.1162 14 (514) 50 1.1182 1.1172 10 1.1130 1.1137 15 (116) 51 1.1108 1.1112 20 1.1083 1.1089 3 (235) 52 1.0940 1.0953 14 1.0941 1.0948 16 (613) *Radiation Cu Kα filtered with Ni (λ = 1.54056 Å) 2 θ = 22–89º. Number of refining cycles: 4, 5, 3. Brushite, CaH(PO4) · 2 H2O, appears sporadically as local, powdery deposits on the surface or in the fissures of the hydroxylapatite crusts. The shining white micro-nodules were collected with difficulty but in a sufficient quantity for the diphractometric analysis: the computed and measured interreticular distances and the recorded relative intensities, with the corresponding Miller indexes, are given in Table 2. 5 Data on the Limanu cave mineralogy 69 Table 2 X-rays diphractometric data from a representative sample of brushite from Peştera Limanu* Crt. Sample PL 6 B Crt. Sample PL 6 B (hkl) no. (hkl) no. dmeas.(Å) dcalc. (Å) I / I0 dmeas.(Å) dcalc.(Å) I / I0 1 7.5461 7.5986 100 (020) 38 1.3720 1.3707 16 (1.10.1) 2 4.9710 4.9265 95 (110) 39 1.3645 1.3674 13 (–1.5.4) 3 4.2388 4.2362 49 (–1.2.1) 40 1.3487 1.3489 24 (–3.8.1) 4 3.8073 3.7993 14 (040) 41 1.3487 1.3466 24 (–4.3.3) 5 3.0271 3.0401 29 (–1.1.2) 42 1.3342 1.3353 20 (0.10.2) 6 2.8453 2.8522 78 (–2.1.1) 43 1.3342 1.3354 20 (1.11.0) 7 2.7959 2.7967 95 (002) 44 1.3203 1.3230 21 (–2.6.4) 8 2.6548 2.6460 18 (–1.3.2) 45 1.3154 1.3173 26 (192) 9 2.5434 2.5329 12 (060) 46 1.3005 1.3019 11 (400) 10 2.5434 2.5514 12 (–2.0.2) 47 1.2819 1.2832 22 (420) 11 2.4735 2.4633 1 (220) 48 1.2819 1.2820 22 (–4.5.1) 12 2.1127 2.1181 6 (–2.4.2) 49 1.2705 1.2693 9 (–4.5.3) 13 1.9682 1.9729 33 (–2.1.3) 50 1.2541 1.2516 16 (093) 14 1.8502 1.8520 18 (–2.3.3) 51 1.2478 1.2476 9 (–2.11.1) 15 1.8021 1.7975 18 (–2.6.2) 52 1.2352 1.2340 21 (233) 16 1.7841 1.7903 5 (–181) 53 1.2298 1.2316 27 (440) 17 1.7841 1.7788 5 (–1.7.2) 54 1.2240 1.2251 20 (–1.10.3) 18 1.7337 1.7388 11 (–2.7.1) 55 1.2240 1.2242 20 (064) 19 1.7337 1.7308 11 (152) 56 1.2173 1.2179 32 (282) 20 1.7142 1.7105 21 (–341) 57 1.2173 1.2178 32 (114) 21 1.6888 1.6938 4 (251) 58 1.2112 1.2116 24 (332) 22 1.6667 1.6648 7 (–2.5.3) 59 1.2112 1.2104 24 (390) 23 1.6454 1.6421 20 (330) 60 1.1728 1.1747 8 (–4.7.3) 24 1.6256 1.6300 23 (181) 61 1.1666 1.1686 6 (381) 25 1.5496 1.5535 16 (222) 62 1.1614 1.1595 12 (–3.4.5) 26 1.5496 1.5514 16 (–2.0.4) 63 1.1441 1.1443 19 (0.13.1) 27 1.5396 1.5347 14 (280) 64 1.1441 1.1439 19 (2.11.1) 28 1.5046 1.5074 11 (350) 65 1.1403 1.1406 16 (1.13.0) 29 1.4669 1.4643 1 (242) 66 1.1403 1.1394 16 (–4.6.4) 30 1.4587 1.4549 2 (321) 67 1.1354 1.1343 16 (–1.9.4) 31 1.4587 1.4597 2 (–2.9.1) 68 1.1287 1.1288 18 (–4.1.5) 70 Gabriel Diaconu, Ştefan Marincea, Delia Dumitraş 6 Crt.