They are totally free. They look perfect for interface design.
1.262 minimalist icons
We present a collection 1.262 minimalist icons perfect for any project, commercial or non-commercial, organized in several categories (multimedia, navigation, symbols, transport, culture, documents, work, devices, buildings, food, education…), a product of the imagination of the Icojam guys.
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The icons are perfect for the interface design thanks to its small size (40 × 40 pixels) and its monochrome appearance, which allows them to be easily adapted to the specific needs of each user. They are distributed in format PNG and with a license that allows them to be used in commercial and non-commercial projects as many times as we want.
Downloading the icon pack can be done from the following link: Eldorado Mini Free.
More information - Metrize Icons, amazing free Metro (Modern UI) style icons