Filled in \diamond without XeLaTeX

Question

I am looking for a filled-in version of the \diamond (⬦) command. More specifically, I'd like a filled-in version that is

1. the same size as \diamond,
2. centered vertically in the same way as \diamond.

I think the Unicode symbol I am looking for is 02B25 (⬥), but since I am not using XeLaTeX, I couldn't find a way to load this symbol. I couldn't get \DeclareUnicodeCharacter to do what I wanted it to do, but this may be due to my ignorance of how to use the command.

Note that the 'diamond' talked about in the accepted answer here is not what I'm looking for, as that diamond shape is different (⬧). There is an answer at the bottom of that page that seems to do what I want, but running that code gives me an error, as I commented there.

I tried the following ugly workaround:

\documentclass{article}
\usepackage{graphicx}
\usepackage{amssymb}

\newcommand{\blackdiamond}{\rotatebox[origin=c]{45}{$\vcenter{\hbox{$\scriptscriptstyle\blacksquare$}}$}}
\begin{document}

\[
    \diamond \blackdiamond
\]

\end{document}

The result is close, but not exactly what I wanted, due to the resulting symbol being slightly larger.

I'm sure there must be a better way of shrinking the symbol down in a less hacky way than I did above, which should be more flexible to give what I want too.

Answer 1

The \diamond symbol, as defined by amssymb is an operation symbol, but apparently you want it as an ordinary symbol.

\documentclass{article}
\usepackage{graphicx}
\usepackage{amssymb}

\newcommand{\whitediamond}{\mathord{\diamond}}

\newcommand{\blackdiamond}{%
  \mathord{%
    \sbox0{$\diamond$}%
    \resizebox{!}{1.125\ht0}{%
      \raisebox{\depth}{\rotatebox[origin=c]{45}{$\blacksquare$}}%
    }%
  }%
}


\begin{document}

\[
{-} \whitediamond \blackdiamond {-}
\]

\end{document}

Should you want both to be binary operation or relation symbols, change accordingly \mathord.

This can be adapted if you also need the black symbol also in superscripts or subscripts.

Alternatively, you can import the single symbols from stix2.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}

%%% from stix2.sty
%\DeclareSymbolFont{symbols4}{LS1}{stix2bb}{m}{it}
%\stix@MathSymbol{\mdblkdiamond}{\mathord}{symbols4}{"E0}
%\stix@MathSymbol{\mdwhtdiamond}{\mathord}{symbols4}{"E1}
\DeclareFontEncoding{LS1}{}{}
\DeclareFontSubstitution{LS1}{stix2}{m}{n}

\newcommand{\blackdiamond}{{\text{\usefont{LS1}{stix2bb}{m}{it}\symbol{"E0}}}}
\newcommand{\whitediamond}{{\text{\usefont{LS1}{stix2bb}{m}{it}\symbol{"E1}}}}


\begin{document}

\begin{gather*}
{-} \whitediamond \blackdiamond {-}
\\
\scriptstyle {-} \whitediamond \blackdiamond {-}
\end{gather*}

\end{document}

Answer 2

The stix2 package splits the Unicode Stix two math font in to Pdftex compatible fonts and gives them TeX names compatible with unicode-math.

The unicode math names for U+2B25 and U+2B26 are \mdblkdiamond and \mdwhtdiamond

\documentclass{article}

\usepackage{stix2}

\begin{document}

$\mdblkdiamond + \mdwhtdiamond$

\end{document}

Answer 3

A poor man's solution could be not rotate \square but a framed color box and to avoid any difference with \diamond, make the white diamond also with a rotated framed color box.

With the default font, the result could be almost identical with most font sizes, although with tiny fonts the fake diamonds are a bit smaller, and with huge fonts you can notice that are sharper, as showed in the MWE below.

Also, with other fonts you will need adjust the xy rotation to control the vertical position, but well, on the other hand, you can make blue diamonds, which are much more expensive. ;)

\documentclass{article}
\usepackage{graphicx,xcolor}

\newcommand{\newdiamond}{%
\mathbin{\rotatebox[x=0ex,y=1ex]{45}{%
\resizebox{.8ex}{!}{\fboxrule.3pt\fboxsep1pt%
\fcolorbox{blue}{cyan!30}{}}}}}

\newcommand{\blackdiamond}{%
\mathbin{\rotatebox[x=0ex,y=1ex]{45}{%
\resizebox{.8ex}{!}{\fboxrule.3pt\fboxsep1pt%
\fcolorbox{black!30!blue}{blue}{}}}}}

\begin{document}

\fontsize{5pt}{5pt}\selectfont \({-} \diamond\newdiamond\blackdiamond {-} \)\par
\fontsize{10pt}{5pt}\selectfont \({-} \diamond\newdiamond\blackdiamond {-} \)\par
\fontsize{15pt}{10pt}\selectfont \({-} \diamond\newdiamond\blackdiamond {-} \)\par
\fontsize{30pt}{10pt}\selectfont \({-} \diamond\newdiamond\blackdiamond {-} \)\par


\end{document}