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Phase relations, compositions, and modes of two natural primitive alkaline basalts were determined through experiments performed at 0.8 GPa, temperatures between 1000 and 1310 °C, and nominal water (H 2 O i) contents varying from < 1 (natural water rock content) to 6 wt.%. The two natural samples used as starting material are high-Mg, moderate-K, alkaline basalt scoria clasts (Mg# = 0.68-0.66,  alkalis = 4.4 wt.%) dispersed within the hydromagmatic tuff of the Solchiaro eruption (Procida Island, southern Italy). These samples are considered representative of parental magmas feeding the Phlegraean Volcanic District, which includes the Campi Flegrei caldera and the Procida and Ischia islands. The composition of the experimental phases has been compared with that of natural rocks to constrain the early stages of crystallization of poorly differentiated magmas from the Phlegraean Volcanic District. Our study shows that the liquidus temperature at H 2 O i < 1 wt% is ~1300 °C whereas with water contents between 1.5 and 3 wt.%, and between 4 and 6 wt.%, the apparent liquidus temperature decreases of about 50-100 °C, respectively. Under natural water conditions (<1 wt%), the liquidus phase is clinopyroxene, followed by olivine and Cr-spinel and, then, by plagioclase. The increase of H 2 O content in the system enhances olivine stability along with clinopyroxene at the liquidus temperature. The 4-6 wt.% water bearing experiments show evidence of H 2 O saturation at 1100 °C, with olivine being replaced by orthopyroxene later joined by pargasitic amphibole and minor amounts of oxide starting from 1080 °C. The composition of glasses in the experiments with low H 2 O i content is consistent with the trachybasaltic products of Procida; glasses obtained in the runs with 1.5-3 wt.% water resemble the trend formed by the shoshonitic products of Campi Flegrei. The water-saturated experiments produced variably alkali-depleted residual glasses whose composition converges toward the subalkaline field. The compositions of the experimental clinopyroxenes match well those found in the Campi Flegrei products for which we have estimated crystallization

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